They were right; the end of the world came with a whimper and not a bang. Castiel had always known it would. Humans would have destroyed themselves, had they been given the chance, long before the sun expanded or polar icecaps melted.
But they hadn’t had the chance; Heaven had taken that away from them, which was something he’d never thought he’d see. He also never thought he’d be down here when it happened. That he’d be fighting alongside the human’s last defence. Or that he’d even care. But he was and he did and he was sat there staring at the reason why. Their fearless leader, Dean Winchester.