Spoilers ahead! Plot points are revealed here, I'll put the deeper plot points in spoiler boxes.

Time travel features heavily in the plot of *Endgame*. Correct me if I'm wrong, but the MCU seems to subscribe to the [many-worlds interpretation][1] of quantum mechanics. This makes any alterations to the past fine, and the "present" people making those changes return to the future they left from unaffected.

So, the plan is:
>! pop into the past to gather the Infinity Stones, wield them to perform a reverse snap, then pop them right back where you found them as if they'd never left at all.

This plan succeeds. However, as a result,
>! the pre-snap Thanos journeys into the future to protect the job he has yet to do, and is defeated in the process. This means that, although the Stones are placed back in their respective times (the Cap's last job before retiring), there's now a universe short of Thanos.

So, my question: **is there now a universe out there in which many of the Avenger's adventures didn't happen (anything after 2014, I think that's where Thanos travelled from), and the snap never occurs, while at the same time there is a universe (the one we see in the films) in which all of the events of the MCU films transpired?**

  [1]: https://en.m.wikipedia.org/wiki/Many-worlds_interpretation