In a report from Vanity Fair on the secrets of the Marvel Universe, it was stated that all of the contracts of the original Avengers actor’s end after Avengers 4 in 2019.
As reported in the article :
After Avengers 4, an ambitious multi-franchise crossover movie slated for release in 2019, at least some of the original characters who sit at the center of the billion-dollar Avengers team will be hanging up their capes and shields. That’s partially because the Marvel contracts with the actors who play them—Evans (Captain America), Ruffalo (Hulk), Downey (Iron Man), Johansson (Black Widow), Hemsworth (Thor), and Renner (Hawkeye)—are coming to an end.
For many, Avengers 4 will be their swan song, and after which they will finally end their superheroics. There is a chance some actors will renew their contracts, as talks of new movies have been discussed, including a Thor sequel and a Black Widow solo movie.
But if it is the end, the stars are definitely going out as a team, based on a quote from Chris Hemsworth on the actors being together:
“I thought, Could somebody take a photo of this? We’re all aware that this is going to be the last time we get to hang out like this.”
No matter what happens for the actors though, it’s quite obvious the MCU will be completely changed after Avengers 4. – Jacob Campbell
Source: Vanity Fair
Avengers: Infinity War hits theaters May 4, 2018
Avengers: Infinity War – As the Avengers and their allies have continued to protect the world from theaters to large for any one hero to handle, a new danger has emerged from the cosmic shadows: Thanos. A despot of intergalactic infamy, his goal is to collect all six Infinity Stones, artifacts of unimaginable power, and use them to inflict his twisted will on all of reality. Everything the Avengers have fought for has led up to this moment – the fate of Earth and existence itself has never been more uncertain.