The Wakanda Files, a new in-world book about the technological aspects of the MCU, reveals that Tony Stark already knew about the ramifications of time travel before the team started their journey in Avengers: Endgame.
When Earth’s Mightiest Heroes traveled back in time to get hold of the Infinity Stones, the Ancient One warned Bruce Banner that this would create alternate timelines and rupture the balance of the multiverse. Luckily for the people who had been dusted away 5 years before, the two eventually reached a compromise, as Hulk promised that they would return the Stones back to their original reality when they were done with them, which Steve Rogers took care of after the Battle of Earth.
According to the newly released Wakanda Files, though, written by T’Challa’s sister, Shuri, Iron Man already knew what would happen if they went through with their plan. In a message he leaves for Banner, Stark speculates: “Altering events of the past could never affect the continuous loop. Though, it could create tangential split-timelines.”
Of course, it only makes sense that the smartest man in the world would predict such an outcome, but Tony doesn’t seem fazed by the notion at all. “Let’s not worry about that for the time being, right? One reality at a time. For all our sanity,” he further notes.
Still, he couldn’t have possibly known for sure what would happen. Fortunately for them, though, Banner came up with a solution and the plan proceeded without too many complications.
Of course, Avengers: Endgame was pretty vague about the rules of reality, so there’s still a lot that we don’t know. Hopefully, though, future MCU movies like Spider-Man 3 or Doctor Strange in the Multiverse of Madness will give us a more fleshed out resolution.