Here you are, preview clips for "The End." I'm warning you right now, I instantly busted out in tears over Clip #3. Here's the official description courtesy of Warner Brothers:
Still estranged from Sam, Dean is visited by Zachariah (guest star Kurt Fuller) who continues to pressure him to fulfill his destiny and become a vessel for the archangel Michael so that he can defeat Lucifer. When Dean resists, he is thrust five years into the future to see the consequences of his decision - and a ravaged, desolate post-apocalyptic world. Also stars Misha Collins as Castiel and also guest stars Rob Benedict as Chuck Shurley. "The End" was written by Ben Edlund and directed by Steve Boyum.