If Hiddleston can be convinced to come back to the MCU - and gets his desire to do something different and unexpected - there's nothing to say he's going to make it out alive. He will in fact perish at the end of Ragnarok if rumours are to be believed, which you have to think is a fitting end for the villain with more lives than a cat. Could an angry Thanos be the one to kill him? Might he sacrifice himself again heroically (don't count on it)? The Evidence Ragnarok culminates in the death of basically all of Asgard's residents: it's a very necessary part of the plot. And the arc of Loki and Thor is very much like the Voldemort/Harry Potter, Joker/Batman, Vader/Skywalker dynamic: neither can truly live while the other survives. And then of course there's the issue of Skull Island. Previously Hiddleston was an up and coming actor with a lot of time on his hands for lesser roles, but his profile has evolved considerably since the first Thor movie and he's now a big time A-lister with limited time. How the hell is he going to film both Ragnarok and the King Kong prequel at the same time?
