No. No, no no no. No, he knows where this is going. He's worked it out already, just by feeling it out, by the knowledge that there's a thread that represents Castiel's life, and it's long, but even Dean can feel where it ends.

And I'll reap God, too, he thinks, and feels like he's going to be sick all over the ground.

"So what, they offered you the big chair and you didn't learn from last time?" It's bitter, acidic, and he can't stop himself from saying it, from spitting the words at Castiel's face, furious that he'd betray them like this.