There's been rumors going round that castiel won't be in season six, but I was on twitter and a link came up about supernatural spoilers. And this came up

"Producer Phil Sgriccia also announced that angel Castiel - played by Misha Collins - will return in the next season." yay!!!

I don know why it says return, but I don't know what happened in the last 5 episodes of season 5 because I haven't watched them yet. Soo.... Yay !!!! Cas rules !!!!