Well, the set shots from Avengers 4 are reportedly filled with people in old outfits.
Whether Thanos nukes the timeline, the heroes give up on beating him in the present and try to alter the past to do it, or it is some weird montage where Stark gets the gauntlet and tries to come up with a timeline with a happy ending, remains to be seen.
But I'm convinced the MU looks way different after Avengers 4. There's too many big names whose contracts are up and the fact that out of the numerous Marvel movies in the pipeline post-A4, only a handful have announced casts (Dr Strange 2, Black Panther 2, (some of) Guardians 3) means that all bets are of for who or what survives past A4. (Again, I'll be shocked if Cap makes it out of Infinity War alive.)