[The following contains major spoilers for Avengers: Infinity War. Turn back now if you somehow haven’t seen it yet.]
With the spoiler disclaimer out of the way, let’s get right to it: Half of the entire universe gets wiped out by Thanos at the end of Avengers: Infinity War, with nearly all of the Guardians Of The Galaxy, the Black Panther, and—most heartbreakingly—Spider-Man all getting dissolved by the power of the Infinity Gauntlet. Of course, while anyone who has read a comic (literally any comic) can guess that those deaths will be undone somehow, a number of other big Marvel Cinematic Universe characters got taken out even before the Mad Titan had a chance to snap his fingers. Some fans are theorizing that those deaths are more likely to stick, even though the Infinity Gauntlet storyline from 1991 found an easy way to reverse everything Thanos did, and now one actor is suggesting that he really is done with the MCU:
That’s Idris Elba saying goodbye to Heimdall, his character from the Thor movies (and one of Thanos’ first victims in Infinity War), which seems to imply that he won’t be coming back for Avengers 4. However, other than some reshoots that are happening in the fall, most of the filming for Avengers 4 has already been done. That means Elba could just as easily be indicating that Avengers 4 is the end of his time as the all-seeing guardian of the Bifröst—but it seems like it’s the end either way.
On another note, if Elba really is done, Heimdall’s death being permanent would probably be the least surprising of the pre-Gauntlet Infinity War deaths. His character has had fewer and fewer things to do with every appearance he makes, and now that Thor’s new axe weapon can open the Bifröst, Heimdall is even more superfluous. If Tom Hiddleston tweets a goodbye to Loki, then we can start believing that some of these deaths are going to stick.