I kind of really want Dean to make it his mission to save the angels/Heaven next season.
Something about the Righteous man leading the fallen angels back home.
BUT! In the season 9 finale!
Dean has got the final piece that will magically give all the angels their grace back and slingshot them back upstairs, and just as he’s about to put in the piece to send them all back (it’s a MacGuffin, play along, people! Moose is off doing Moose things - babysitting Crowley or something), Cas places his hand over Dean’s and Dean looks up at him.
“What, Cas? What is it?”
“I want you to know …” Cas looks down and uncurls his fingers, where there’s a small vial, glowing bright in his palm. Dean got that back from him at the start of the episode, along with the last spell ingredient he needed so he could send the angels back up. “When you send the angels back to Heaven, I — I will not be going with them.”
Dean is, of course, flabbergasted and sputtering. ”The angels? What — I — Cas, man, I — all of this… I thought you wanted —”
“I know where I belong, Dean,” Cas says quietly, looking up to meet his eyes. ”I finally know where I belong.”
“So… so you’re saying…” Dean begins, not willing to believe it.
“Do you wish for me to stay?” Cas asks, looking nervous even though he’s already made up his mind.
“Cas,” Dean sighs, shoulders slumping. He reaches out with his free hand and grasps the back of Cas’s neck, pulling him in to rest his forehead against Dean’s. ”That’s all I ever wanted.”
“Then I’ll stay,” Cas whispers and Dean’s eyes flutter closed and he nods.
“Ready to send ‘em home?” Dean asks, after he’s made sure to clear his throat in a suitably manly way.
Cas nods and they place the final piece to send the angels back together, Dean’s arm wrapped around Cas’s shoulders, holding him close and tight.