The next 4 years of Marvel Studios' cinematic calendar are set in stone. We already know that Captain America: Civil War is coming next April, followed by a couple of sequels (Guardians of The Galaxy 2, Thor: Ragnarok) and new entries (Black Panther, Doctor Strange, Captain Marvel). The third phase of the Marvel Cinematic Universe culminates in May 2019, when the second part of Infinity War saga hits theatres.
After that, July 2019's Inhumans will be the only movie left on the currently announced slate. This date is still obviously quite a ways away, but you have to wonder if Marvel will have anything left in the tank for phase 4 and beyond.
In a recent interview with Slashfilm, Avengers producer Jeremy Latchem addressed these concerns. He says that Infinity War will indeed be a last hurrah of sorts for the current roster of superheroes. However he stresses this won't be the end of the franchise, saying that the concept of the Avengers will never go away. He proceeded to cite instances from the comic books where the team's composition was altered:
The team will be evolving. One of the things we loved in the comics is the rosters always changing and you could pick up a new issue of the comics ten years later and you don't recognize the people on the cover. But the ideas and ideals that make The Avengers still exist, and I think that's part of what makes this culmination will be: we're seeing this version of the team doing this thing to save this universe, this galaxy, however you want to put it, and we'll see where this goes.
Marvel still has an extensive list of heroes to bring to the big screen, and there's always the possibility of bringing some of their TV properties over to the big screen. It's safe to say we'll be getting new Marvel films well into the next decade.
