I'm glad they permadeathed her. I got so tired of people dying on this show and coming back, it cheapens death. I don't get Cas' obsession with bringing her back to life, though. He's an angel, he knows she's in Heaven. She will live in paradise forever. Her sons will be up there with her in fifty years at most, and probably a lot sooner given their lifestyle. Your loved ones die, you just deal with it.
I wouldn't call it dark side, he's just a force of nature without his soul, not good or evil. He's like a walking hurricane. Dangerous, sure. I like Jack, I'll feel bad if things end badly for him.