How would the evil guy bolster his power by killing Death? Is he just planning to increase his reputation, or does he think that Death has magic and that he can absorb it by defeating him? Or does he get more powerful by killing anything? I'm not sure about the magic in the Dresden Files so I don't know if a temporary death would do anything or if the bad guy could absorb Methos's quickening.

Shouldn't Bob be in there somewhere? As I understand it, Bob is supposed to be the voice of reason so he probably tried to convince Dresden not to remove the tag. I don't know what else he'd do though. The only way I can think of to protect Cassandra over the long-term is for her to be tagged again, but maybe she can be taught enough to protect herself?