MCU: 10 Marvel Characters Who Will Definitely Die In Phase 3
6. Loki
Why He Has To Die
Having pulled a fast one at the end of The Dark World and pretended that he was dead, Loki seems to have reverted to type, mischievously stealing Odin's throne and kicking off the events that lead to Ragnarok and the near-destruction of Asgard.
At some point though, we know he's going to align with his brother again (as per the Doctor Strange post-credit scene), and that means he will be seeking some forgiveness for his crimes. In story-telling terms, killing him off would be the most fitting resolution to his arc, and since his death was integral to the Ragnarok comic arc, it'd make sense he won't make it out of that film alive.
When It'll Happen
The end of Thor: Ragnarok, nailed on.
How He'll Die
Having accidentally handed Asgard to Hela by trusting her too much to share the spoils of war (probably), Loki will no doubt have a major change of heart before realising he needs to help Thor find Odin and stop the madness. And him actually sacrificing himself to save Thor as he pretended to in The Dark World would be a lovely end to his cycle.