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.