Well, Firestorm was basically two characters; Ronnie Raymond and Jason Rusch; basically, a lab accident caused them to fuse together into at an atomic level into the superhero called Firestorm. They could live their own lives, but the schtick was, generally, that, when they were in superhero form, Rusch was in control while Raymond was his co-pilot, of sorts; talking in his ear. It's nothing to do with Supernatural, but I just liked that idea that, after a demon was cured, he might not be exorcised, so, if his host was still alive, you could have an interesting dynamic, as, naturally, a reformed demon isn't going to want to do anymore harm (I.e. maintaining the "hostage" situation going on in the host's body).
I agree about Dean, as well. Dean's always been my favorite, but, after rewatching everything in a row, it kind of forced me to look at his progression objectively, and, when that moment came around, I literally slapped my head. Hell, the issue could've solved itself, when you think about it. Had Sam closed Hell, they'd have been free of that issue, and, with Heaven also being closed for business, they could've still kept the character around (albeit a little "ghostier"
). End of the day, what Dean did was stupid. I could imagine Bobby saying something to him along the lines of "your brother was gonna close the gates of hell. That's like...unlimited brownie points for those winged douchebags. Not only was he gonna save a helluva lotta people, but he might a made his way offa this rock and finally got some damn rest. Ya Idjit."