The Marvel star says he learned from his wife, producer Susan Downey, saying, "you don't know what or how you're gonna end until it is."
"That takes a lot of the edge off," Downey said. "She's learned how to be like, 'You won't know until you're there, so you're wasting your time on that equation. That's not on the test.'"
"I could project all kinds of stuff. I could get into the black dog. Whatever you want," he continued, teasing a continued tenure: "Or I could stay, spiking it in the end zone until I have to be carried off. I'm looking forward to whatever resolution is in the cards."
Infinity War will reintroduce Tony Stark as still struggling to get over his feud with Steve Rogers from Captain America: Civil War, with that movie's ramifications at the forefront of the Avengers threequel.
Despite their emotional and physical confrontation at the end of Civil War — where Stark learned Cap was aware his best friend and war buddy Bucky Barnes (Sebastian Stan) was used as a tool by Hydra to kill Howard and Maria Stark — Rogers entrusted Stark with a cell phone to be used should he ever need his old team mate's help.
Tony isn't over the sting of that revelation, Downey said, calling it a betrayal on par with that of Stark's mentor-turned-villain Obadiah Stane (Jeff Bridges) in the first Iron Man.
"To me the big question is could he ever in clear conscience pick up that flip phone Cap sent him at the end of Civil War. That is really it. For me I think back to Obidiah and that deception," Downey said, reasoning "it's why [former Journey lead singer] Steve Perry never went back to Journey."
Asked if Tony and Steve spend much of Infinity War separated, Downey admitted, "I don't know."
"I feel like my instinct would be to bust his jaw. All I know is that there's something about being on camera with [Chris] Evans. I hate to say it, but I don't know what I'm gonna do when he's not Cap anymore," Downey said.
"I look at him and think this is the truest, most down moral psychology I've ever seen and then they go, 'Cut!' and Chris is like, 'Hey buddy, I gotta get out of here.' I'm like, 'You wanna go to dinner?' 'Nope.' 'Okay! Love you! Love you, Cap! I mean, Chris!'"
Avengers: Infinity War opens April 27.