There's enough visual stimulation onscreen to potentially lose track of the Infinity Gauntlet during this sequence. On a certain level, it's worth wondering why the Avengers didn't have a plan to destroy the Infinity Stones and the new Gauntlet right after using them, but we know destroying the stones is a complicated process and they weren't expecting Thanos to slip through time with his space ship. There's really no time and the plot needs to keep moving. In the midst of the raid on the Avengers' compound, Hawkeye attempts to protect Hulk-gauntlet, but he eventually gives it up to Nebula, who he doesn't realize is actually the evil Nebula. Thanos gets ahold of it, and after swatting away a wide range of Avengers, he's ready to once again unleash its terrible power. This time he plans to kill off all of humanity -- not just half. He realizes there's really no upside to leaving all those leftovers around.
When he's about to pull of his final deadly snap, Thanos declares in his deep baritone, "I'm inevitable." But then, in yet another twist, he tries to do the snap, which fails when he realized the stones are no longer in his glove. Instead, Tony Stark reveals that he's constructed his own backup, quasi-improvised Infinity Gauntlet glove-like device, which he uses to pull the Infinity Stones toward him. (When did he make this and was he always planning to unveil it? That one's difficult to answer.) Now, he's got the power. "And I'm Iron Man," he quips in a call-back to the surprise ending of the first Iron Man movie from 2008, the film that kicked off the MCU over a decade ago. Then, he snaps.
If you don't totally get the rules of the Infinity Gauntlet, that Iron Man snap might be confusing. It's not totally unreasonable to wonder, "Wait, did Tony Stark just kill off half the population again?" Here's what you need to remember: Once you have all the Infinity Stones in the Infinity Gauntlet, the glove functions a bit like genie's magic lamp, and the snap performed by Stark has a different aim than Thanos' evil snap or Hulk's reviving snap. He uses it to wipe out only Thanos and his armies. Of course, he pays a heavy price for performing this act of mystical destruction, and, lacking Hulk's gamma-resistant strength, the snap kills him. Following Stark's funeral, the ending of the film finds Captain America traveling back through time to return the Infinity Stones to their rightful time periods, creating a version of the present where there are no longer any Infinity Stones. (Remember: the decapitated Thanos destroyed the ones he used.)
This means that Avengers: Endgame, the likely swan song for Robert Downey Jr.'s Iron Man and Chris Evans's Captain America, is also probably the last time you'll be asked to care about Infinity Stones and the Infinity Gauntlet. Were they sometimes shoehorned into otherwise zippy action-comedies? Sure. Did every aspect of them always hold together over the last decade of plotting? Not exactly. But they served their purpose of creating a sense of scale and connectivity to this gargantuan narrative system. Whatever combination of new Marvel superhero movies, sequels for familiar characters, and heavily hyped Disney+ shows follow, they will probably focus on a different set of objects for fans to obsess and theorize over. There's always a plot demand for more items to pursue, more mysteries to crack, and more evil to be undone. Still, as far as cinematic MacGuffins go, the Infinity Gauntlet and the Infinity Stones had a historic run.