The apocalypse is over and Dean is safe and happy in his room. He's sitting on his bed, smiling the most genuine smile he's ever put on his face in a long time, and wearing a jacket that's at least two sizes too big. But that's okay because, well, who knows? Perhaps he's shrunk a bit, or maybe Castiel's healing had a weird side-effect, or maybe he's just always been this size and finally noticed. But it's okay. Everything's over now, he's done -with angels, demons, the end of the world; all of it. He'll just sit here forever talking to his brother, listening to his music, doing what he wants to do for the first time in his life.
There's a sudden knock at the door but he doesn't look up or even acknowledge the creak of hinges as it opens just a crack. He merely sits, calloused fingers playing with the amulet around his neck, and continues to talk to his brother.
Outside, the doctors watch with mournful eyes and broken hearts as their newest patient calls the adjacent wall Sammy.