While Avengers: Endgame is barely over a month away, we still have no idea what's going to happen to the Marvel Cinematic Universe after it's over. Yes, we're going to get a Spider-Man movie, but how will the events of Endgame change the characters and stories we're going to get in Phase Four of the MCU? We don't really know the answer yet, but one of Avengers: Endgame's writers wants us all to know those changes are going to be real and they're going to be big. According to Christopher Markus...
The MCU continues to exist. What happens to be in it is a fluid and evolving thing where, because it's all connected, you can't reboot one. All the parts have to work together. Things continue, but like life, losses are real, and change is real.
We have some expectations of what some of the big changes that are coming will be. Certain actors are set to leave the MCU and as such those characters may die or be written off in some other way. Maybe the hero and the costume will live on being worn by another, maybe not. However, if you were expecting things to largely go back to something resembling "normal" once these few changes happen, Christopher Markus' statement would seem to discount that idea.
The Marvel Cinematic Universe was an attempt to take the long term continuity and crossover aspects of the comic book world into the cinema. In the comics, while each character is largely left to their own devices most of the time, things do happen in one part of the world that can have repercussions on others. The MCU, because there are far fewer movies than there are issues of comic books, feels these changes in a much greater way.
However, Markus' comments to Empire would seem to spotlight one major place where the MCU and comics differ. It's an area I had wondered about myself previously. In the comics, while things do go through major upheaval from time to time, the world always returns to the status quo eventually. Steve Rogers has died and lost his powers at different points and others have taken up the shield, but eventually Steve Rogers is Captain America once again. That's not going to happen in the MCU.
Whatever changes we see at the end of Phase Three, as Christopher Markus says, will be real. If Steve Rogers dies in Avengers: Endgame, he's almost certainly going to stay dead. If Robert Downey Jr. is too expensive to keep in the MCU now, that's not going to change in the future. And at some point these actors will simply not want to return to these roles, even if they're offered all the money in the world. Eventually, these characters will change for good and there will be no return to the status quo.
While this is, on the one hand, going to be frustrating for those that lose their favorite heroes, it's also incredibly exciting. Major, real change in a persistent universe is something that Marvel has never really tried in the comics. How well will it all work? What new exciting characters or major changes to existing ones could happen that will take stories in entirely new directions? We'll begin to find out very soon.