There was no shortage of mistakes made by the heroes in Avengers: Infinity War, from Gamora giving up the Soul Stone's location to Quill blowing it on Titan. The last and perhaps most tragic came when Thor dealt what he thought was a killing blow, driving Stormbreaker into Thanos' chest instead of his head, allowing the Mad Titan to still deliver the universe-balancing snap. Needless to say, the Avengers will have to learn from these mistakes if they hope to prevail in Avengers 4, starting with going for the head. One fan has taken this quite literally and created some fan art where Iron Man does just that. Take a look:
That is pretty gruesome and also a really cool piece of art from ultraraw26. Iron Man looks triumphant here, holding up the trophy of his victory but still wearing some majorly scarred armor, souvenirs of a battle well fought. Thanos' lifeless head is wearing an expression of surprise, confusion and perhaps fear. He must have known that he was finally about to meet death right before it happened. Clearly Iron Man got the memo that you've got to cut the head off the snake and not give him even a moment's opportunity to use the gauntlet. Probably good that he learned from Thor's mistake because I can totally see Tony Stark taking time to gloat over a foe he thinks is vanquished. (You really don't want to be the Oberyn Martell of the MCU.)
As we've seen, the MCU heroes are not above killing their enemies and it's hard to argue Thanos doesn't deserve it. This is a guy who wiped out half the universe, snuffing out an incalculable number of lives. Trillions? Quadrillions? More? Decapitation couldn't happen to a nicer guy. If the Avengers are to defeat him in Avengers 4, you've got to think they will want to eliminate him as a threat for good and be absolutely sure he can't return to his genocidal ways. Correcting Thor's mistake would be one way of doing that, although I suspect this might be a bit too dark for a Marvel movie, even if Iron Man ripping his head off would be cool.
I imagine the ultimate defeat of Thanos will not come through brute force or separating his head from his body, but through strategy and whatever Doctor Strange has planned. Maybe Captain Marvel will just wreck him or maybe Avengers 4 will follow the comics. There are some potential clues to Thanos' defeat in the commentary track on the Avengers: Infinity War Blu-ray, but we won't know for sure until next year.