SPOILER WARNING: The following article contains major spoilers for Avengers: Infinity War. If you have not yet seen the film, please bookmark this page, and save the read until after your screening!
Looking ahead to Avengers 4 after the end of Avengers: Infinity War, it's clear that the heroes of the Marvel Cinematic Universe are in serious trouble. Not only are their numbers seriously depleted thanks to Thanos killing half of all life in existence, but the great threat they find themselves facing has the power of a god thanks to the assembled Infinity Gauntlet. From an outside perspective, the whole situation very much seems hopeless and impossible, our favorite characters seemingly doomed to live in a Thanos-controlled reality, but there is reason to be optimistic. After all, comic book history does provide some clues as to how the Mad Titan can be defeated.
In a sense, it comes down to one word: experience. Thanos may view himself as destined to wield and utilize the Infinity Stones, making himself the most powerful being in the universe, and he certainly demonstrates a keen intellect, but his greatest weakness is still his nascency. There is a lot to being a god, and he will need time to fully understand not only his abilities, but his place in the universe. In the past, this has been something that the Marvel heroes have been able to exploit, and they could do the same when it comes to defeating Thanos on the big screen.
The original Infinity Gauntlet series progressed to see Thanos go head-to-head with some of the most powerful cosmic beings in the universe, organized by Silver Surfer and Adam Warlock among others, but by the end of the conflict it wasn't about strength -- partially because the Mad Titan proved to be stronger than any and all other god-like entities. Instead, victory was achieved because the enemies of Thanos (read: just about everybody) were successful in taking advantage of his lack of experience with an overabundance of power. Following an epic battle, Thanos manages to become the literal center of reality, leaving his "flesh" form behind -- and while he believes that this move sheds him of all vulnerabilities, the exact opposite is actually true. He forgets that his true power ultimately exists with the use of the Infinity Stones, and when he leaves his body he opens the opportunity for the Gauntlet to be taken right off his hand.
Because Avengers: Infinity War isn't a direct adaptation of the comics, and because there are some key differences between the Marvel Cinematic Universe and the source material, we don't expect Avengers 4 to feature this exact same conclusion -- but a version of it is certainly still on the table. After all, Thanos is going to be in a strange headspace when we next see him, having achieved the mission he worked towards his entire life. As mentioned earlier, his next move could involve further exploration of what it means to be a god, feeling out his capacities and limitations, and it could create a very important opportunity. If the heroes can get Thanos to leave his corporeal form and remove his gauntlet, they could put the Infinity Stones in responsible hands and un-do at least some of the damage caused by the fascistic purple alien.
If this is the route taken, who could this hero be? In the comics it's Adam Warlock, but that option seems to be off the table. Could it be Iron Man, explaining why Doctor Strange was willing to trade the Time Stone for his life? Could it be Captain America, who has proven to have an unbreakable moral compass? Or perhaps will it Captain Marvel, who is said to be the most powerful character in the Marvel Cinematic Universe. Any of them wielding the Infinity Gauntlet could have fascinating effects.
Of course, all of this is just speculation for now, and we still have about 12 months before we get any firm answers. No matter what, though, regardless of Avengers 4's fidelity to the comics, the movie should feature some major surprises and important consequences for the future of the franchise.