Iron Man's death, as well as Steve Rogers' retirement. Although Thor's godly nature could allow him to keep fighting for millennia, Chris Hemsworth will probably hang the cape and move on long before Thor grows old.
Phase 1 of the MCU established that Asgardian gods are just very powerful aliens. Characters like Odin, Thor, and Loki can live for thousands of years and withstand plenty of damage, but in the end they're still mortal beings. In Phase 4, Thor: Love and Thunder confirmed that Asgardian royals are full-fledged deities, and it introduced the Norse version of the afterlife, the mythical Valhalla. While the MCU's rules for entering Valhalla aren't yet clear, it's safe to say that even after death, Asgardian warriors can live on eternally.
Valhalla seems like an ideal resting place for Thor after everything he's been through. However, it also gives Chris Hemsworth a unique challenge. Either the MCU sends Thor to Valhalla when Hemsworth is ready to retire the character, or future MCU movies just stop following Thor as he continues to live for millennia. Either way, the MCU must ignore the possibility of Chris Hemsworth's return knowing that Thor is still out there somewhere. This lack of a definitive end to Thor's life means that Thor's MCU story is never really over, as a future installment could technically revisit him at any time.
Will Thor Ever Go To Valhalla in the MCU?
If there's any MCU character that earned his spot in Valhalla, it is definitely Thor. Whether Thor will ever go to Valhalla is not a matter of if, but of when. Thor: Love and Thunder could only be the beginning of Thor's second MCU trilogy, at the end of which Thor could make the ultimate sacrifice to prevent another Ragnarök. Alternatively, Thor could outlive the MCU's next generation of Avengers given that he's already used to seeing everyone around him come and go while he stays roughly the same. The MCU's Thor could also end up becoming the wise old King Thor, a mirror of his father Odin, and only die after thousands of years and hundreds of allies being born and dying all around him.
Whenever the MCU decides to let Thor go, it's certain that he earned the reward of reuniting with Odin, Frigga, Heimdall, and Jane Foster in Valhalla. Perhaps Thor will make his promise to Loki, "the sun will shine on us again", come true in the afterlife. And while the MCU's Valhalla can leave Thor without a definitive farewell similar to that of Iron Man, Captain America, and Black Widow, it also provides plenty of options for Chris Hemsworth's final outing as Thor. Hemsworth could reprise his role anytime — either resting in Valhalla or coming back from the afterlife temporarily — or he could decide to move on from the MCU for good. Whatever the case, Thor: Love and Thunder has signaled Thor's final resting place early in the Multiverse Saga.
