From what I remember (and I could easily be confused as well), he killed Opera because he wanted to save his lady - sacrificing Opera for her (the way he tried to get Gateau to sacrifice Carrot (or was it Carrot supposed to kill him? Now I don't remember. ^_^;;; ). But anyway, it turns out he killed Opera for nothing since he couldn't save his lady entirely, so she kept returning to cat form when his powers were low (lack of moonlight, something like that). She was mad at being kept isolated by him, so she wanted him dead (spinning the tale that he was the one who turned her into a cat). Once he realized she didn't love him at all (just his stage), and that he'd killed for someone who could care less about him, he stopped fighting, died, and let her live her life on the stage (as a cat - which he'd done everything possible to avoid).
>.< Sorcerer Hunters has some twisted plots for pointless angst's sake (pointless for the people involved since it always turns out worse than what they were trying to avoid/protect/etc), this is one of those.
[And I'm not sure I remember who Bagel was, but if it was the one who had the Lord kill Opera, then yeah, I'm pretty sure he's dead. I don't remember which one killed him (Gateau or Croissant), but he wasn't an issue anymore.]