An Alternate Ending, if Season 9 was to be the last:
"What about you?" She asks, "Without your own grace, you’re going to die."
Cas blinks emptily, nodding once. Just once. “So I’ve heard.”
"What are you going to do, brother?"
Castiel brings himself to his feet, one corner of his lip quirking upwards—weak, forced, but well meant. “Pursue my last pieces of happiness.”
- - -
Castiel finds himself in the bunker, in a familiar room.
He lays himself down on the other side of the bed, tucks himself beneath still but familiar arms, splays his fingers against the slight dip of a familiar chest. Holds him close.
"I’ll watch over you."
He closes his eyes.
(They will not open again.)