Empire Movie Podcast that Tom Hiddleston will unfortunately not be reprising his role as Loki in the upcoming sequel.
When initially asked about his progress on the movie, Whedon gave a similar answer to what we've heard for some time: "I've
turned in a first draft, but the story is very set. Everybody's very
much on board with the exact movie I'm trying to make which is what
worked the first time."
Whedon also became the bearer of bad news: "Immitating
what I did before is the surest way to do it not as well. Second of
all, and Loki is not there to say those terrible things."
How will this effect the happenings in "Thor: The Dark World" is yet to be seen, but Thor does threaten/promise to kill Loki if/when he betray him in the recent trailer for the film