I had a player who used to regularly send me complaints. I told him more than once that I wasn't changing x, y or z to the way he wanted it and I understood if he didn't want to play any more. It turned out that he did want to continue playing but also had a pathological need to be a whiny little bish at the same time. Anyway it got to a point I told him to stop complaining or I'd uninvite him, a couple of weeks later he was still creating drama so I banned him.

tl;dr instead of enabling Bob, tell him GTFO. I would absolutely retcon the encounter to say Bob died rather than use his spells, the party won anyway, congratulations everyone except Bob.