< Avengers: Infinity War Is Now...
Arguably the most surprising survivor of Avengers: Infinity War was Nebula. When Thanos completed the Infinity Gauntlet and killed half of all life in the universe, Nebula was someone most fans assumed would be a goner. In fact, it wouldn't have shocked anyone if Thanos had killed his adopted daughter even before he claimed all six Infinity Stones. But when the Mad Titan snapped his fingers and fulfilled his dream of universal genocide, Nebula escaped death. Could this mean her comic book storyline might still happen?
Infinity War is purportedly based on Jim Starlin's The Infinity Gauntlet, but it is actually more akin to Gauntlet's prequel, The Thanos Quest, which is about the purple nihilist's murderous journey to assemble the six Infinity Stones. Infinity Gauntlet saw Thanos already in possession of all of the Stones, with Marvel's superheroes and cosmic beings trying to relieve him of his weapon of ultimate power. As for Nebula, she appears in Gauntlet as a minor player but then ascends to become a threat as nearly severe as Thanos himself.
In the comic, Nebula (who is Thanos' granddaughter and very different from her mechanical movie incarnation played by Karen Gillan), is used as a pawn by the Titan to impress Mistress Death, his paramour. The original reason Thanos went after the Infinity Stones was to please Lady Death by killing half of the living beings in the universe. Instead, Thanos succumbed to the god-like power the Infinity Gauntlet granted him, and Death spurned his pledges of love.
Nebula was revived by Thanos as a burned-up shell of herself just so he could torture her to entertain Death, but his would-be lover was not amused. Nebula lingered through most of the story half-forgotten in the background. When the superheroes and cosmic entities waged war with Thanos, the Titan got distracted. Seizing the opportunity, Nebula took the Infinity Gauntlet from Thanos, healed herself with it, and used it to undo his work, restoring the people who had been killed by the finger snap. Adam Warlock attacked Nebula from within the Soulworld of the Soul Stone and she had to surrender the Gauntlet, which eventually ended up in Warlock's possession. Nebula was imprisoned, while Thanos went off to live the quiet life of a farmer, temporarily rid of his lust for power.
Infinity War did adapt a few elements of Infinity Gauntlet. Nebula was still tortured by Thanos, but for two reasons: because she had tried to assassinate him, and to manipulate her sister Gamora into revealing the location of the Soul Stone. Afterwards, Nebula freed herself and joined the Avengers and Guardians of the Galaxy to fight Thanos on Titan. She never makes a play to capture the Infinity Gauntlet for herself, but that doesn't mean it couldn't happen in Avengers 4.
It seems like Gamora's prominence in Infinity War replaces Nebula's in the comic, but Gamora's role was very different: with their backstory as his favored child in the forefront, Thanos sacrificed Gamora's life to gain the Soul Stone. However, Gamora's survival in the Soulworld didn't happen in the comic. While Nebula and Gamora's sibling rivalry was settled in Guardians of the Galaxy Vol. 2, hating Thanos is the one and only thing they agree on, and it doesn't mean that Nebula is now a goody-goody. If anything, she's probably got even more anger built up after being horribly tortured by Thanos.
It's hard to tell what Nebula knows about the nature of the Soul Stone, and she may not suspect Gamora lives in the Soulworld. Regardless, revenge against Thanos is the only thing Nebula lives for, and she's now one of the positives of the Avengers' situation because she's the only living being who knows Thanos and where he went after he won. Still, Nebula can't be entirely trusted.
Perhaps the only way to undo Thanos' mass murder and save Gamora is to take the Gauntlet away, which is something Nebula will attempt to get revenge. As in the comics, she likely can physically wear the glove, but it probably won't take much for that kind of power to go to her head and have her declare herself "Omnipotent Nebula." Avengers 4 could come down to the two sisters having one final row over their father's gauntlet, with the fate of the universe in the balance.