ok so here's what actually happens:
the gang go into the ud to do their plan and everything, and the military notice after a delay and start preparing to go after them
everything goes more or less the same up until el enters the abyss, except during the confrontation with the soldiers el manages to fight through the suppression to save kali so she only gets shot nonfatally. she's still taken out of the fight though and hopper has to bring her down to the truck to patch her up.
el hops into the abyss where the gang are trying and mostly failing to fight the giant mindflayer monster and confronts henry. he gives her another speech about how the world needs to be reborn cuz it sucks or whatever and she tells him to fuck off and uses the memories of all of her loved ones to overpower and kill him--but its all just a little too easy.
they rescue all the kids but they're a little catatonic and weird. they manage to get them all through the gate anyway but when they go to load them into the truck uh oh, the military are here. and they've already got everyone left behind in custody. which means no one is manning the bomb. uh oh.
the gang try to explain what is happening and how they need to destroy this place and save the world but dr. kay isn't hearing it. she just wants the girl. and she better come quietly or they're all gonna die here. mike/the party/hopper exclaim that they'd rather die than give her up, but el reveals herself anyway and tells dr. kay that she'll go with her peacefully if she lets everyone else go. kali freaks out. mike freaks tf out. dr. kay doesn't really say anything but orders a solider to detain her, but as he goes to do so there's a rumbling in the sky. the tears start ripping open. bits of the abyss terrain start raining down. demogorgans start appearing from the trees. and through one massive, apocalyptical whole in the sky: the mindflayer reanimated. and it's fucking pissed.
the soldiers immediately forget about el and everyone else and start blasting that thing and all the other monsters with everything they've got. the scene descends into absolute chaos, but within it all our heroes manage to regroup and make their way to the trucks to gtfo. the only person that notices is dr. kay.
the military's attacks are barely managing to even distract the mindflayer, and it slowly starts making its way towards the nearest gate, which starts to react as it gets closer. oh shit. el notices this and then remembers, there's no one up there to man the bomb. oh shit. she grabs mike and asks him how long it will take them to drive out of here. and how many songs long that would be. mike figures out what she's plotting, freaks out again, begs her to just come with them. she says collapsing the ud is the only way to destroy that thing, and she can get to the bomb the fastest. she has to do this. it'll be ok. mike lets her go, but he's not ok about it. she runs off to the lab, everyone else drives off. dr. kay is the only one that notices.
el makes her way to the top of the lab by scaling the outside of the building, using her powers to grab the walls and launch herself (or maybe navigates the melted stairs with her powers idk). when she gets to the top she surveys the area and tries to calculate exactly how much time she should give the bomb, and also resolutely considers waiting to set it off manually to guarantee it goes off at the exact right time. it looks like she's about to make a decision when suddenly she's hit by an anti-psychic suppression ray from a little handheld gun by dr. kay. who has obviously gone a little insane about still trying to capture eleven. they have a whole confrontation. dr. kay gives her a speech about how she's a dangerous thing that the government created and owns and if she was really capable of caring about those friends down there she'd just turn herself in and also whether she likes it or not dr. kay is gonna make her super army of physics that she'll control better this time and then then she will become the most powerful military force in the world or whatever. and this whole speech is so ridiculous that its the final nail in the coffin that convinces el that she's absolutely not giving in to this bullshit and is going to fight for her right to live, so she tells her to fuck off and smacks the weapon out of her hand and flings her off the top of the lab with her powers, then sets the bomb to about half of the record to give herself time to escape.
so while that was all going down the gang were driving like hell to get to the gate. they're weaving in between the mindflayers legs and the military's fire and everyone's screaming and its chaos. one of the military vehicles notices them and decides to try and stop them, but before they're able to do much damage the car mysteriously flips over on its own and blows itself up, and then there's a heavy thud on the roof of the truck. everyone screams, but then el pokes her head down in front of the windshield to tell murray that she saw monsters up ahead and to just keep driving. sure enough, demos come out of the woods to start jumping on the van. el starts ripping them off. hopper and nancy shoot a few through the walls of the truck. then, with the gate in sight, the bomb goes off. it shakes the ground so violently that murray swerves and el falls off. robin notices and yells at him to stop, but the gas pedal presses itself down to the floor and they speed toward the gate where a petition has been setup. the blocks fly away as they approach and they make it through the gate with time to spare.
as soon as they've slowed down mike throws open the doors and runs out, yelling and searching for el. he runs towards the gate and sees her a little ways off, exhausted but running for her life. behind her the ud is collapsing in a tornado of debris and military personnel, and right when she's yards away from the gate, the mindflayer is completely absorbed. el falls to the ground like someone just shot her in the head. mike screams her name and rushes after her. lucas follows without a second thought. nancy screams after them. suddenly will falls ill too, and so does kali and the kids. dustin looks around. oh shit, they killed the host. mike and lucas rush into the hurricane and grab el. the others rush forward to help pull them out. the collapsing flurry is feet behind them. they're pulled across the threshold at the last second and tumble to the ground. el is still writhing in pain, unresponsive.
the first to wake up are the kids, who finally cough up the mindflayer particles they were injected with, but this time instead of flying away they kinda come out as dust and disintegrate. will is next, and wakes up shaking in his mother and brother's arms. mike is too busy screaming and begging el to wake up to notice. eventually hopper joins in, then lucas. we get a glimpse at what el is experiencing, and basically, because el and the other psychics' powers came from the mindflayer, after it was killed it also killed parts of them and with the last of its strength and control is trying to drag them down with it by forcing them to succumb to despair and die. but, obviously, el pushes through all the trauma and violence the mf was responsible for, towards the voices of her loved ones and the dreams for what she wants out of life, and after an agonizing final battle, she finally breaks through and wakes up. everyone is ecstatic, but before they can celebrate for too long el calls out for kali, and drags herself over to help her make it out too. she gives her a little speech about how their lives are worth fighting for, and she doesn't know what's going to happen next exactly but they'll never get to be happy if they don't even try. she just has to fight. and sure enough, kali soon sputters back to life. holy shit they actually did it.
everyone finally breathes out and starts celebrating. holy shit. they actually did it. but then some government guys show up. oh shit. but they're being led by owens actually. oh shit? and he's walking around like wtf just happened here? did yall just save the world? oh shit that's actually hype. so dr. kay was a freak and i came here to stop her but looks like she's already dead so that's cool. oh shit is that 008? oh shit she was shot. don't worry we'll get her some medical attention. yes, you can follow her to make sure we don't get up to anything. so like i'm tryna cover this all up so ur not in trouble but if you don't mind i do have some questions and would like to set up some cover stories and maybe make you sign some documents. also do yall still have powers? no? ok chill once we confirm that we can get yall some IDs. but also maybe you should leave the midwest for a while.
so owens gets everyone's phone numbers and full government names and social security numbers and sends them off to iowa or whatever. and its very sad because we have to leave our home behind but its ok because we all made it and we're all together. kali sticks around with everyone for a bit but eventually goes back to england to find her family because i said so. anyway its epilogue time.
el and mike are almost late for graduation because they're hanging out and are terrible at leaving each other's company bc of the Trauma. they're having a conversation about their future and mike asks her what she wants to do after school. el replies she's never thought about it. all she's ever wanted was this (*gestures vaguely at her current life situation*) and didn't even think she would get that. mike tells her this is just the start and they can do literally anything they want now. el thinks about it and remembers a documentary she watched once with three...beautiful misty seaside cliffs in ireland. and she's always dreamed of being there. mike says he'll start saving up for plane tickets now.
at graduation, el and max sit together in the stands because they were both held back a year (or two) due to coma and never really been in school, which max laments but also expresses how grateful she is that el and her will still be together. el agrees but also expresses how weird it still is to be able to be in huge crowds out in the world like this. max sympathizes and expresses how grateful she is that she's here. they hold hands in best friend solidarity.
because they're at a new bigger school dustin only got salutatorian, and after he gives his own nice little short speech he hijacks the end of the valedictorians' speech for his little hellfire antics. the rest of the boys walk across the stage and get their diplomas. mike and el wave at each other from across the stadium.
they go to a graduation party where they hang out and talk about their future plans. then someone remarks that this party is kinda lame and they don't even know the kid that's hosting it (one of dustin's new random friends). mike says he has an idea what they could do instead.
the scene opens with that same sprinkler shot as s1 but its a different sprinkler at a different house. in a different basement but with the same friends, the party plays dnd. the game is a thinly veiled retelling of the events of the finale. after they win mike waxes poetic about where everyone is going to end up after the show. dustin will become a perpetual student. will will find gay culture in the city. lucas and max go to japan for college FUCK YOU ITS MY REWRITE. uh and he and el travel the world looking for inspiration and people to help along the way. then everyone puts their dnd binders away and its all sad, and holly and the kids come down to play, and the party goes upstairs to party just a little bit more before they start the rest of their lives. the show ends on a slowly zooming out shot of them through the windows of the house, laughing and talking. the end. also el's new government name is Elizabeth Jane.
