Originally Posted by herolee10
Loki had placed the Casket onto the device that activated the Bi-Frost Bridge, which is the reason why we saw the place being frozen up with that interesting looking icicle tree inside of it. The casket most likely fell into the darkest part of the cosmos when Thor destroyed the bridge.
I can't believe I missed that after having watched the movie about 10 times. I had always thought he cast a spell to do that.