The character became the main antagonist of The Avengers and was given something of a redemptive arc in Thor: The Dark World.
It makes sense Loki’s original arc for Thor: The Dark World involved the character dying in a heroic sacrifice since it would be hard to completely redeem him following his actions in The Avengers.
Tom Hiddleston has revealed Loki’s fakeout death in Thor: The Dark World was originally written as the end of the character.
Hiddleston also admitted during the interview there were a lot of reshoots on Thor: The Dark World to lighten up the original, darker tone.