Dean refers to Castiel as "Bukowski" after he suggests they consume copious amounts of alcohol and wait to die. Charles Bukowski
was famous for writing novels and poetry dealing with alcoholism, death and many other depressing subjects. See more
So what's it all add up to? It's hard to say. But me, I'd say this was a test... for Sam and Dean. And I think they did all right. Up against, Good, Evil, angels, devils, Destiny, and God himself, they made their own choice. They chose family. And, well... isn't that kinda the whole point? No doubt - endings are hard. But then again... nothing ever really ends, does it?