Avengers: Endgame will not only mark the end of the Infinity Saga, but it will also potentially mark the end of the line for the Avengers' "Big Three"--Captain America, Iron Man and Thor.
Chris Evans' Captain America will likely appear for the final time in the upcoming Marvel film (although it's not confirmed), as Evans has hinted that he's retiring the role. And Robert Downey Jr. has played coy regarding reprising his role as Tony Stark post-Endgame.
Officially wrapped on Avengers 4. It was an emotional day to say the least. Playing this role over the last 8 years has been an honor. To everyone in front of the camera, behind the camera, and in the audience, thank you for the memories! Eternally grateful.— Chris Evans (@ChrisEvans) October 4, 2018
However, the third member of the "Big Three" is making it known that he'll happily return to the MCU. In a recent appearance on The Ellen DeGeneres Show, Chris Hemsworth stated he's definitely open to be a part of Marvel's Phase 4.
“Whether they go off and shoot other things or do prequels or sequels or whatever they can do… Loki, my brother’s come back nine times, three times he dies, so who knows what’s in store for anyone?" Hemsworth said. "Me personally, it’s the best fun I’ve ever had. And I’d be happy to do more if they wanted me. More than happy.”
With Marvel's emphasis on secrecy, it's understandable that Hemsworth isn't confirming he'll reprise the Thor role in the future. However, he seems more open to--and more likely to--return than Evans and Downey.
Based on the way Avengers: Infinity War ended, Thor has some unfinished business with Thanos that will possibly be settled in Avengers: Endgame. The film debuts in theaters on April 26.