Reading this has made me wonder more about the evil (necromantic?) ley line coming out of Demonreach. Have we had a good description of the type of line it is? Is it necromantic? We know it is essentially the "body heat" or evil residue being put of by the prisoners. It seems to be a source of power that Harry could feast on ala "darkhallow" without actually killing anything, and hopefully without any sentience behind it to drive him crazy. But if that were possible than one would think that people would be comsuming the power from all kinds of ley lines to become more powerful, and we don't see that happening. Still, we know he was admonished by the Gatekeeper not to touch that power _yet_ so it will probably play a big role at some point...
Also, I think the roleplaying game paranet files expansion implies that Rasputin became the winter knight for a while. He wasn't a full fledge wizard, but a specialist like an ectomancer, only instead specializing in biomancy or something of that ilk. (I'm going off of memory here) It is implied that with the power of the mantle he might have managed to regenerate himself from being shot in the head. Not a full white council wizard becoming a winter knight, but something close...