I’ve seen a couple of fics where Gabriel comes back to help Cas, but I’d really like to see Balthazar come back.
I can just imagine Cas seeing Balthazar and going, “No, please, not him. Please not him.” Even though he’s never begged, not even when Lucifer puts on Dean’s face and says the most wonderful and horrible things, he doesn’t beg. But he can’t stand to see Balthazar, so be pleads for Lucifer to stop, and it breaks Balthazar’s heart, so he wraps Cas up in his wings, but that just makes it worse. And Cas breaks down and starts begging for forgiveness, even though he doesn’t believe that Balthazar’s real. And Balthazar wraps him up tighter and whispers, “Of course you’re forgiven. It’s okay, Cassie, it’s fine, I forgive you.”
But Castiel never believes that it’s really him, that he’s really alive.