Hi, long time lurker and first time poster here.
-Castiel's Death: It's pains me to say it but the character had become a severely damaged trainwreck, completely lost, ineffective and lacking focus after the S8 finale, the only reason he was still onscreen if you ask me was keeping the fans of Collins happy and the problem mainly stems from the fact that strong Cas and friendly Cas just can't go together for more than a handful number of episodes without severely hindering the tension of the show.
And I'm a fan of the character myself, I do hope we get to see Cas again fully restored for the last season, perhaps as the final aleader of heaven appointed by Chuck and hopefully in form of an Archangel.
-Crowley: I like The character and the actor but I can't really point out why he survived S6 when Cas "killed" him. The character had a very very pointless run between S6 and S12, I thought him eventually becoming human and then dying would be a fitting end for the character and how different he had become after the incomplete cure by Sam but they simply dropped the whole thing together and had him commit suicide as a Demon out of nowhere.
kinda defeats the purpose, doesn't it?
-Alternate Universe: Becareful with that one, hitting zero on interpersonal relations between likes of Alternate Cas and Bobby is a dangerous gamble, it can kill the show, (refer to Fringe season 4), either give us Bobby and Cas or just let them die.
Overall really Cas felt like a loss to me, It was sad to see Crowley go but Cas's death was just hard, he's the third brother, still haven't forgotten about his powerful initial introduction and really wonder how "I'm Castiel, an angel of the lord" became "I'm Cas, the fifth wheel of the coach and still fail at being that"