Warning: This article contains SPOILERS for Avengers: Endgame.
Thanos certainly believed he had destroyed the Infinity Stones in Avengers: Endgame - but did he really? Although Marvel Studios is well-known for playing the long game, they didn't settle on the idea of using the Infinity Stones until partway through production of The Avengers. Director Joss Whedon knew he needed a cosmic villain to be the true mastermind behind the Chitauri invasion, and he got the go-ahead to run with Thanos. At around the same time, Marvel looked back at their scripts and realized they had an awful lot of MacGuffins that be retconned as Infinity Stones.
The Infinity Stones have been central to the first three phases of the MCU, so much so that Marvel boss Kevin Feige now calls them "The Infinity Saga." Each one of the Infinity Stones has driven the narrative of different films; the Tesseract has been so prominent that it's appeared in more Marvel movies than Captain America. It's important to note that the Infinity Stones of the MCU are slightly different to the Infinity Gems of the comics; in the comics, each Infinity Gem represents a different aspect of reality, whereas in the MCU they are relics that predate the universe itself.
Avengers: Endgame apparently completes the story of the Infinity Stones, with Thanos believing he's destroyed them. The Avengers believe him, so much so that they plan a "time heist" to steal the Infinity Stones from the past in order to use them in the present. The Avengers use time travel for the first time. But was Thanos right?
How And Why Thanos Destroyed The Infinity Stones
Avengers: Infinity War ended with Thanos triumphant, succeeding in his insane plan to erase half the life in the universe. His mission accomplished, the Mad Titan retired to his garden, believing the cosmos would find a new balance. But according to Avengers: Endgame, Thanos came to realize that the grief-stricken peoples of the universe would never simply accept what he had done. They would strive to find a way to undo it; that would inevitably lead them to seek out the Infinity Stones. So long as the Infinity Stones still existed, they would serve as an irresistible temptation. So Thanos decided that the Infinity Stones had served their purpose in the grand order of things, and had to be destroyed. He used the Infinity Stones themselves, causing a discharge of cosmic energy that rivaled the snap itself.
A precedent was clearly established in Avengers: Infinity War, where Scarlet Witch had the power to destroy the Mind Stone. According to Vision, she could do this because her power signature is very similar to the Stone's own. It implies that only a power related to the Infinity Stones is able to destroy them. In theory, then, Thanos could indeed do this using the Infinity Gauntlet. Certainly the energy discharge suggests that he successfully destroyed them. From an out-of-universe perspective, this is quite a smart move on Marvel's part. Just as Thanos believed the Infinity Stones would serve as a temptation to anyone who wanted to undo the snap, so they would serve as a temptation to future scriptwriters. If they wanted to increase the scale of their film, they could simply reintroduce an Infinity Stone.
But Can The Infinity Stones Be Destroyed?
While there are subtle differences between the Infinity Stones in the films and the comics, there is indeed a comic book precedent for the destruction of the Infinity Gems. The most notable of these was during Jonathan Hickman's New Avengers run, which actually inspired a large chunk of the plot of both Avengers: Infinity War and Avengers: Endgame; it introduced the Black Order, for example, and featured Thanos' forces invading Wakanda. At one point, Steve Rogers attempted to use the Infinity Gauntlet to prevent the collision of two dimensions. He was successful, but at a cost; it proved too much even for the Infinity Stones. Five of them shattered, and the Time Stone vanished into the timestream.
Hickman was telling a complex, drawn-out story in which the entire Multiverse itself was collapsing; the destruction of the Infinity Gems was a sign of the Multiverse's instability. Hickman's story ended in the Secret Wars event, in which the Multiverse collapsed into Battleworld. When the dust settled from Secret Wars, the Multiverse was recreated - and a stable universe required recreated Infinity Gems. In the comics, the Infinity Gems are tied to aspects of reality itself, and when reality stabilized they simply returned into existence.
It's true that Thanos, like Scarlet Witch in Avengers: Infinity War, believed he had destroyed the Infinity Stones; the spectacular release of energy suggests that he was right. But these are cosmic objects that are barely understood, even by Thanos, and it's by no means certain that the Infinity Stones can be destroyed, permanently. They could have very well been recreated elsewhere, just as in the comics. After all, energy may have been released, but that doesn't mean it couldn't come back together again.
What Could This Mean For The Future Of The MCU?
It's certainly possible that the Infinity Stones are gone for good; at the very least, Marvel clearly want to take them off the table for a while, which makes sense given they've driven the MCU's narrative for the last 11 years. But that doesn't necessarily mean that the Infinity Stones will never return. But one thing has changed.
Before Thanos, the Infinity Stones were viewed as legends, fables that were told to children. Even Thor believed the Aether was just a myth, tied to the bedtime horror-stories of the Dark Elves. Only a few beings realized that the Infinity Stones truly existed, and several such as the Collector dedicated their lives to attempting to find them. After Thanos, though, nobody would ever think the Infinity Stones were mythical. The entire universe was affected by the Decimation, and no doubt Captain Marvel discussed what had caused the snap when she visited other worlds. She'd have told people that the Infinity Stones were destroyed. But if even one Infinity Stone was found, everyone would realize she was either lying or just wrong. Post-Thanos, everyone knows what the Infinity Stones can do, and even that their power can be combined. The resurgence of the Infinity Stones would be viewed with terror.
On the flip-side, though, if the Infinity Stones do still exist, then it means that Gamora and Black Widow can potentially be resurrected. In the comics, anyone who's sacrificed to the Soul Stone winds up living in the Soul World inside it; and it's entirely possible to both escape from, and be rescued from, Soul World. That may not be a hypothetical situation; Avengers: Endgame's final scenes set up Peter Quill's quest to find Gamora. Guardians of the Galaxy Vol. 3 could easily serve as setup for the return of the Soul Stone; and if one Infinity Stone returns, then it means they're all out there.
