When Castiel hears that laugh, he's expecting Dean to finally relent, to let him in and let him help. It won't be the same, Castiel won't be the person who Dean's spent two years grieving, but at least it would be something.

But it doesn't play out that way. Dean's face falls, and as soon as Castiel sees that he knows he's lost his last chance.

He could keep pushing, of course, but what would the point be? He'd only be causing Dean more harm, and doing that knowingly, and that's not something he's willing to risk right now. Dean's made himself perfectly clear, and Castiel's out of viable options.

Castiel stands there, listening to the persistent banging of that hammer for at least ten seconds.

He doesn't say anything, just does as Dean's says and leaves with a flap of his wings.