So, I've been thinking about the season finale for a while, and here is what I think has happened.
Castiel's vessel has been possessed, much like Lovecraft's maid was, by a more powerful being. Now there are plenty of options for that powerful being.. but seeing as how it's pretending to be Cas, I'm going with Nyarlathotep. He's a powerful Outer God in the Cthulhu myhthos who has already walked on Earth. And he's the most likely to just fuck with people because he can. I'm going to continue to think about this possibility and maybe go insane (like you do when investigating eldritch subjects)
This brings me to my second tin-hat theory. That D/C shippers are going to get our chance to put our money where our mouthes are. Sure, I think a majority of us are just into the D/C relationship and would have shipped it no matter Castiel's package. (though his Misha package was quite satisfactory and awesome) Now if he has been displaced from his Jimmy meatsuit, and I'd rather that to him being stuck in a vessel with Nyarlathotep or being destroyed flat out, that means he needs another vessel. And we all know that Castiel doesn't care. Leaving an opening for Castiel to come back as a girl, and for Misha to be on the show at the same time. Who knows what sexyfuntimes could come from that?
Now, this finale was pretty devastating to our ship. With a few cannon volleys they took out our sails and possibly weakened our hull, but I believe we can overcome this adversity through fic and clinging to the subtext that is really just text. And you'll see me, should even more dire things occur, playing RockBand as I sink into oblivion with my ship.