if buffy was written by the poi writers jesse would have haunted the fuck out of that narrative. there wouldn't even need to be flashbacks with him (requiring actor availability). you just would have been reminded basically every single second that willow and xander used to have a third friend, who wasn't buffy.
which ofc would have added to buffy's push and pull of friendship/alienation. she doesn't really belong. she's just slipping into the role of a ghost.
there's so much messed up about how xander is portrayed and how he warps the narrative (you could write entire books on this) but just leaning into BECAUSE JESSE would have fixed so much of this. why is he so completely obsessed with the idea that vampires, all vampires, regardless of soul status must ontologically die? because it means jesse was already dead when he accidentally killed him. (remember that, he literally accidentally killed him. ofc you don't remember that bc the show never reminds you because it completely forgets about jesse.) it wasn't his fault. it wasn't his fault. every single thing about the way he approaches the world has to warp around making sure that single moment wasn't his fault.
meanwhile willow responds the opposite way with trying to seek extra agency, hyper-agency even.
hell. these opposite reactions from willow and xander could even lead to a sense that they're drifting away from each other, which could even explain the stupid s3 suddenly they're kissing each other plot !! 'oh no we're drifting away and you're the only thing left of my old life and i have to keep you. kiss you? wait no. wait yes? wait fuck? im so confused.' not the weirdest thing that's ever happened to a 17 year old.
and then ofc the series could just pick up more and more hauntings from there. jenny callendar. kendra. god, even professor walsh barely even haunted the narrative after being killed. what were they even doing. you'd think a show about killing the undead might, perhaps, benefit, from some thematic use of guys haunting the narrative. but no. canonically basically only tara gets to. come on. come with me to this world where i could fix buffy.