An interesting theory I saw somewhere on line is that the next movie will essentially have two main story lines: the remaining Avengers plus the others working to get the stones back from Thanos with the folks who disappeared forming the second story line. These folks are actually trapped inside and have to do something to work to get back, essentially forming a "New Avengers" to move forward with after some combination of Tony/Cap/Black Widow/Thor/Hulk go away and/or are killed off.
This seems to make a lot of sense to me, both for the IW4 next May and for Phase 4 and beyond, giving Marvel some story flexibility for future movies.
This seems to make a lot of sense to me, both for the IW4 next May and for Phase 4 and beyond, giving Marvel some story flexibility for future movies.