If anyone ever told Dean Winchester it would have ended like this, he would never had believed them. He had told Sam about it once, "sand in our toes and matching Hawaiian shirts" he had said, but he never for a second truly thought it would happen. In reality he knew it was going to end ugly, bloody and sad. That's how it always ended for hunters, on a pyre covered in salt, if you were one of the lucky ones, if you had someone with you to do it. Sometimes you just disappeared, sometimes it was worse, sometimes you didn't. And through all of that Dean had hoped that however he ended, Sam would get his happy ending (and Dean always smiled a little at that) and Cas, well he didn't know what would happen with Cas. Cas was eternal, he was going to outlive them all, even if he didn't want to. All Dean hoped for was that one day Cas would see that he was as much family as Sam ever was. But this, the sand and the ocean and the happiness? This was unexpected.
Dean had expected there to be a battle, a grand eons old battle between good and evil, between brothers, between the dark and the light. Lucifer had taken Sam, just like he always said he would but this time Dean had a weapon and he knew exactly who needed to wield it. And just like Sam had said all those years ago, when he wasn't Sam, it didn't matter what they did, they would always end up here.
And he was right, as the Prince of Lies so often was, but the bloodthirsty, earth shattering bone breaking battle never happened. Sure there was a fight, Michael said there would be, but it was short and brutal and after years of terror and torture, Lucifer was finally gone. His burnt out body lying on the ground, a hole in him where Dean had plunged the blade they had waited for for so many years, and the Michael Sword standing there having done its job. Dean stood in front of Sam and watched him laugh and laugh and then descend in heart wrenching sobs, the whole time Michael whispering to him about their deal. And then he was gone, and he was just plain old Dean Winchester again. And Sam wasn't a vessel and he wasn't a vessel and Michael did everything he promised he would and they sat in that room and cried over everything that they had taken from them.
It was a miracle but Michael came through, and every last monster and vampire and dark shadow that had followed the Winchester boys their whole lives was gone. It was like the sun had at last come out and they could finally live their lives. They didn't get back everyone they lost, that wasn't part of the deal, but they were finally free. Team Free Will was finally, fiercely, irrecoverably free. So here they were, two broken boys and their fallen angel finding their way. They had no path to walk, no road to follow, no dark night to creep into and no disturbed town to drive out of. They had nothing but time and Dean knew what to do with it. So sand and Hawaiian shirts and time and beach chairs and beers and time and fishing rods and time. So much time.
Dean picked up his rod and walked down to the shore line, swung the rod behind him and cast that line out as far as he could see. He got a bite and wound it in. He could get used to this. And cast his line again. And then cast it again, Sam and Cas were laughing and calling out to him to cast his line out. I'm trying Dean thought, stop laughing at me. Cast it out they kept yelling and laughing. But not laughing, but laughing but not laughing but still yelling. So much yelling cast it out Dean, cast it out. Dean stopped throwing the line to look back at them and they both just stood there. Sam and Cas standing there, not yelling anymore, screaming, like their chests would burst, cast it out Dean, cast it out. And then silence, silence like the world was ending and he finally saw them, he finally heard them one last time. Not cast it out. Not cast it out at all.
Cast Him Out.