So I know we collectively hate time reset/dimension wipe theories about S5, but.....maybe it does need to happen?
Assuming the last couple seasons of ST weren't some elaborate manifestation by Mike to deal with the trauma of losing Will, there are some problems that seem like they can't be fixed without some kind of a reset.
El. Just El in general. Owens was able to give her a fresh start, a new name and a chance at being "normal", However, too many people know about her telekinetic abilities and the ability to open and close gates to the Upside Down. I think she would be in danger of being kidnapped and studied/used as a weapon forever. She can't just kill off/destroy the entire U.S. government (if only), so her file will probably be available for years and even if not, enough people know about her existence that bad actors could target her.
Now that the UD is merging with the RU, will it be contained to Hawkins? Will it spread throughout the country? The world? Even if it is all a hive mind, if they killed Vecna and somehow closed all the gates (it exhausts El to even close one), would those spores or whatever still be floating around and infecting things in the RU? How could they ever get rid of all of it or ensure that it was all contained in the UD?
As long as both the UD and El exist, even if Vecna is defeated, scientists/governments will always track her because they will want to know more about/study/find lucrative applications for the UD. They would still want to use El or use her to find their own way to open gates.
If all this is true and Will/El/the Party need to destroy the UD to make sure no one ever crosses over again, is that really fair? Even if Vecna harnessed the dark particles and created dangerous monsters out for blood, it is hinted that the UD is not inherently malicious. Sure, the Party want to kill Vecna, but if he's gone and the creatures are just minding their own business, would they be fine with destroying it?
And even if they wanted to, could they? How? If it turns out we're right about Will having powers, how would he use them to destroy the Upside Down? I highly doubt his powers would be like El's or involve gates. If he had some kind of creation powers, would he just recreate the UD with glowy light particles and make it beautiful? But even if he did this, wouldn't scientists still want to find a way inside to study it with El"s gate-opening powers?
On the other hand if he (or someone else) has some kind of time powers, when would they reset it back to? Or what would they go back in time to change? Is there something out of space and time that doesn't belong? (Somehow I am reminded of El saying she doesn't belong anywhere).
If Will or someone else wiped out the dimension that contains the UD (or banished it to another dimension), MKUltra would still have been doing their telekinetic children experiments, right? And if they went back in time, how far back would they have had to go? Back before Henry was taken to Brenner? Would El have been created at all if her mother wasn't part of the MKultra experiments?
Bonus thoughts about a reset: we know how much the Duffers love The Neverending Story. Spoilers for Neverending Story after the cut:
