During its special announcement today, Marvel Studios has confirmed that Thor will return for Marvel's Phase Three. The third Thor film will be Thor: Ragnarok, and will hit theaters July 28, 2017.
Like Captain America: Civil War, the title paints a very clear road for where the cinematic Odinson is headed. “Ragnarok,” a Thor storyline published by Marvel Comics in 2004, was significant for killing off Thor, Asgard, and all of its inhabitants for several years. The story had a lasting impact on the Marvel Universe, removing Thor and his supporting cast from Marvel’s publishing schedule for several years.
As Kevin Feige explained during the special event, Ragnarok is “The end of all things.” Ragnarok, a staple of Thor's Mythological Norse origins, closes the endless cycle of death and rebirth that all Asgardians endure. Essentially, it is the Armageddon for Asgard and all of its gods.
If Thor is to truly meet his end in Ragnarok, it only furthers the rumors that the third Avengers film, now confirmed as Avengers: Infinity War Pt. 1, would feature a new cast of Avengers in 2018.
However, star Chris Hemsworth still has two more Marvel movies to produce after Ragnarok, a per his contract with Marvel studios. Marvel could keep Thor off the board in the two Infinity Warfilms, and have him appear in two more Thor films for Phase 4. But, the idea of Marvel not having Thor in its biggest film yet seems a little unlikely.