Major spoilers for Avengers: Infinity War.
One of the most fascinating twists in Avengers: Infinity War involves Doctor Strange and Tony Stark. Early on in the film, Strange insists that he will sacrifice anyone and anything in order to prevent Thanos getting his hands on the Time Stone. Then, later in the movie, Strange actually bargains with Thanos - he offers him the Time Stone if he leaves Tony Stark alive. It's an unexpected moment, and you see that shock on Stark's pained face. Why has this happened?
It's heavily implied that this is a result of Strange's use of the Time Stone. The someday Sorcerer Supreme has clearly learned a great deal about the Time Stone between Doctor Strange and Infinity War; he's able to use it to glimpse millions of different futures, in order to formulate a plan that could defeat the Mad Titan. Shockingly, Strange reveals that he's only seen one possible future out of 14,000,605 in which Thanos was defeated. At the film's conclusion, as he fades from existence, Strange tells Tony; "There was no other way."
Strange, it seems, had looked beyond the cliffhanger ending of Avengers: Infinity War. He knew that what has been done by Thanos can yet be undone, whether through time-travel or use of the Infinity Gauntlet itself. But what if it isn't just the Avengers losing that's necessary, but them losing in a specific manner, with him actually having to save Tony Stark to fix Thanos' wrongs.
Tony Stark is Just What The Avengers Need After Infinity War
Most superheroes tend to be reactionary in nature. A villain masterminds a terrible plot, and the hero reacts to it, working to defeat them. But Tony Stark is different. He's not just a "billionaire genius playboy philanthropist," he's also a futurist. Marvel tend to use that term to describe a hero who intuitively recognizes the threats and possibilities of the future. The MCU has faithfully reproduced that element of Stark's comic book character; one glimpse of an alien invasion in The Avengers was enough to tell him that another attack was coming.
A futurist is a dangerous force, as the MCU has made clear. Believing another alien invasion was on its way, Stark attempted to create a global defense system - Ultron. In Captain America: Civil War, Stark was so focused on the fact the United Nations would push further measures that he sacrificed the Avengers' unity in the short-term.
In the aftermath of Infinity War, though, a futurist is just what the Avengers need. Most of the heroes are reactive, and will find themselves struggling to deal with the reality of what Thanos has done. Tony Stark, however, is the kind of man to look beyond that. A futurist is the only type of hero who can ask; can this be undone? Is there a way we can put this right? No wonder he's the one man Strange needs to keep alive.
Tony Stark Now Knows About Time Travel And Alternate Dimensions
"When did you become an expert in thermonuclear astrophysics," Maria Hill snarked at Tony Stark in The Avengers. "Last night," he responded confidently. There's a sense in which Tony Stark is your stereotype comic book genius; a man so intelligent that he can master an entirely new scientific discipline overnight. It's true that Marvel has since teased that he's not actually the smartest man on Earth; one of Black Panther's producers suggested Shuri is smarter than Tony Stark. But, in this case, Stark has knowledge that Shuri doesn't.
While on Titan, Tony saw Doctor Strange using the Time Stone to view myriad alternate futures. He's smart enough to thus intuit that the multiverse theory is real, and that time-travel is actually possible. If that's the case, it means history can be rewritten. Thanos's victory can still be prevented, made as though it never happened in the first place - or somehow twisted to be undone.
There's a lot of evidence that Avengers 4 is a time-travel film, including set photos that show members of the Avengers wearing what appear to be strange timepieces, including Tony Stark. It's distinctly possible that, inspired by the example of Doctor Strange's sorcery, Stark will be the one who invents time-travel and launches a plan to rewrite history...
Tony Stark, Master of the Mystic Arts
Infinity War and Avengers 4 were filmed back-to-back, and there seems to have been some overlap during filming. That means some of the behind-the-scenes footage already released may actually link in to Avengers 4. Take, for example, mysterious shots showing Tony Stark wearing the Cloak of Levitation on Titan. At the time, it was assumed to be part of an action sequence, but now Strange has been erased from existence it may be something more. Indeed, he wasn't wearing the Cloak at the time, meaning it's still around for Tony to take up.
In the comics, several of Marvel's key scientists have actually dabbled with the mystic arts. Mr. Fantastic, for example, was once given possession of a powerful amulet with which to attack Doctor Doom; every time he confessed his ignorance and the limits of his intelligence, it projected a devastating attack. More recently, the X-Men's Beast has learned quite a few mystic tricks of his own, almost unleashing a Hell-dimension. Even Tony Stark is no stranger to sorcery. A number of comics have suggested there are future timelines in which he actually becomes Sorcerer Supreme. The idea was finally explored in detail in last year's Generations: Iron Man & Ironheart one-shot, which saw Riri Williams meet the 126-year-old Tony Stark. So there's a clear comic book precedent for Stark to begin working with magic.
In both comics and the MCU, magic and science are essentially one and the same. Marvel Studios, in particular, has worked hard to establish a scientific basis for their sorcery. When producing Doctor Strange, Marvel consulted with countless theoretical physicists and experts in quantum mechanics. Given the scientific principles that underpin the MCU's magic, it's hardly inconceivable that Tony Stark would begin to intuit the laws of magic. It's possible this could give him the unique perspective he needs to defeat Thanos.
The Ultimate 'Sacrifice Play'
The currently untitled Avengers 4 is clearly something of a "last hurrah" for the classic team, given most of the heroes from Phases 2 and 3 were erased from existence in Infinity War. With the next movie the true finale, it seems likely that Tony Stark will pay the ultimate price.
That's essentially been Stark's main character arc all along: does he have what it takes to truly be a hero? In the first Iron Man, he revealed his identity when needled by Christine Everhart in a press conference. "I never said you were a superhero," Everhart teased, prompting Stark to out himself as Iron Man. Steve Rogers challenged Tony in a similar way in The Avengers. "You're not the guy to make the sacrifice play," Captain America argued. "To lay down on a wire and let the other guy crawl over you." That question has hung over Tony Stark's entire superhero career; is he able to set aside his own interests, in order to become the hero the planet - in this case, the universe - actually needs?
Ironically, of course, Doctor Strange was making a "sacrifice play" in Avengers: Infinity War himself. He'd seen the future and knew what Thanos would do with the Infinity Gauntlet. When Strange handed over the Time Stone, he was well aware that he would soon be erased from existence. "There was no other way," he concluded, and so he accepted his fate in order to ensure Tony Stark could live on. If Avengers 4 does indeed conclude with Stark's death, there will be a neat inversion to it; Strange embraced death so Stark could live, in order for Stark to die and save the cosmos from the insane wrath of Thanos.