One of the most shocking moments of the first teaser trailer for Thor: Ragnarok was the moment Hela (Cate Blanchett) destroyed Thor's (Chris Hemsworth) beloved hammer Mjolnir. It's not a spoiler for anyone who has seen any footage from this movie so the official social media accounts for the movie and Hemsworth himself posted a little video of Thor explaining what the hammer was to him. We also get some of Korg's (Taika Waititi) dialogue and how funny the character actually is.
— Chris Hemsworth (@chrishemsworth) November 8, 2017
Mjolnir has been destroyed a handful of times in the comics and come back. There have been a few pieces of concept art for Avengers: Infinity War it looks like Thor could be holding up his hammer but it's unclear.
Mjolnir is closely linked to Thor as a character so it wouldn't be surprising if they found a way to bring it back.
Summary: Imprisoned, the mighty Thor finds himself in a lethal gladiatorial contest against the Hulk, his former ally. Thor must fight for survival and race against time to prevent the all-powerful Hela from destroying his home and the Asgardian civilization.
Thor: Ragnarok, directed by Taika Waititi, stars Chris Hemsworth, Tom Hiddleston, Cate Blanchett, Jeff Goldblum, Idris Elba, and Mark Ruffalo. Check it out in theaters now.