Right but the tagline isn't "the end begins", it's "every ending has a beginning" which to me implies that the beginning has significance to the ending.
I can honestly see them wrapping this up by Eleven stopping herself from creating the first tear and somehow sacrificing herself to do so.
How else are they going to close the potential of the upside down always being an ever present threat?
It's effectively the exact same sentiment, just worded differently to sound more clever.
It's important to note that we have yet to see
any actual time travel at this point, just memory viewing and illusion casting. I don't think you can cram time travel into a story like this at the eleventh hour and have it work. Stories fundamentally shatter like glass when you try to force time travel into them unless you wrote them to be about time travel from the very beginning.
Like if Eleven was going back in time to close the original portal, what good would that do aside from negating the entire journey everyone has been on up to that point? Keep in mind, the first tear didn't even create the Upside Down, all it did was send 001 into it. Then later on, she made another portal under Brenner's instruction and then
another one when she connected with the Mind Flayer for the first time the same day Will disappeared.
The Upside Down only became a "threat" per se when Brenner made El start fucking around with it. And having her go back in time and sacrifice herself (somehow) to stop that from happening would still likely result in One killing all the kids in the Hawkins Lab, and Vecna still being created. And who knows if he would've somehow found a way through the dimensional wall anyway? There's too many variables overall and there's no one fulcrum point that clearly represents "the moment everything became inescapably bad" - it took nearly five years for all that to pay off.
Realistically, I think the safest thing they can do
for the story is just have the Mind Flayer's destruction be the end of it. The Upside Down is a hostile dimension, technically, but it's hostile
because the Mind Flayer effectively controls it and is trying to encroach into the primary world. Once Vecna is knocked off the board and the Flayer is dealt with, the Upside Down is no longer an active threat to the world. It's still there, but nobody is capable of bridging the gap between worlds and there's nothing actually useful over there to justify jumping the barrier even if there was someone capable of doing so.
I mean this season has a grandfather clock as one of its main symbols, the upside down looks like how Hawkins did on the day Will disappeared, and Vecna even went "It wasn't supposed to go this way" or some such as if he saw the timeline change suddenly when El overpowered him.
I think the upside-down is literally a parallel universe that will resume when the current universe is destroyed, which will be the start of a new timeline where all this mess didn't happen.
Of course One didn't think it was going to "go this way", because he was confident that his power was enough to accomplish his goals, and he was surprised that even after absorbing the powers of the other test subjects Eleven was still stronger than he was in that moment. It was Vegeta being taken by surprise by the Kaioken Kamehameha.
At the end of the day, I just don't think "we made a new timeline where nothing bad happened" is a satisfying way to end a five-season serialized drama. It's cheap and lazy and makes the entire journey up to this point entirely meaningless.
And you really can't do spinoffs if you do a "we made a new timeline where nothing bad happened". I mean you could try, but nobody would care.
