Dean is going to die.
He knows this. Has known this since the moment he and Sam first learned of Crossroad demons. Back then he hadn't known when or how - but he knew the why. Because it would always be the same:
Sammy. His brother. The boy he raised into a man, who grew to be too tall, and developed a sense of self that never quite fit in with the Winchester clan. Because the Winchester family stopped being about the individual and started being about the cause in the middle of a cool November night long ago. Because while the differences between John, Sam, and Dean were plentiful, they were always supposed to be ignored in the name of a greater good. Of justice. Of revenge. Only that was never for Sammy and Dean knew it. Knew it, and helped to make it happen. Until time passed and Sam had four years of normalcy under his belt - of the apple pie life John had once lived and lost; the life that Dean had long since accepted he would never have.
But none of that matters now, because Dean is going to die and he's already accepted it. Because he would do anything for the brother he raised and fought for. And giving up his life to bring Sammy back from the dead was never a question. It was a fact.