While Marvel is keeping tight-lipped on what’s in store for Avengers 4, leaked set photos from last year seemed to indicate that time travel would play a role in the movie, although that’s been called into question since directors Joe and Anthony Russo implied that the recreation of certain major events is actually due to Tony Stark’s BARF technology.
Still, if the Battle of Sokovia is being “revisited” in some form or fashion, then it would make sense to see Quicksilver there.
Assuming that Thanos’ Infinity snap didn’t accidentally bring a few people back to life, one would imagine that either Quicksilver’s possible return in Avengers 4 is either due to a different type of resurrection or that we’re seeing him in a different capacity.