According to rumors and the prediction, the movie will be released in 2022-2023. If there will be anything more about the release date then I'll let you know.

Is Tony Stark coming back?

"It's an animated version of all the characters we know and love from Marvel and this episode included the Grandmaster and Iron Man, so Robert Downey [Jr.] will do a voice for that." Unless Marvel has had a massive change of heart, Downey Jr. will be back as Iron Man/Tony Stark for one last time.

Who is replacing Tony Stark as Iron Man?

The Marvel Cinematic Universe is always moving forward. Marvel's Phase 4 is taking fans to the new Marvel Multiverse and it is doing it all without the two characters who led Phases 1-3: Tony Stark AKA Iron Man (Robert Downey Jr.)