Haha, that's a lot of wolves! They should at least eliminate the threat of farmers/hunters, hopefully the kamikaze dwarves too.
Petrus should be the only one who poses a real threat. The angels / some of the NPCs will be difficult but probably not too dangerous. I would recommend staying outside of the Cathedral, near the library. The mystic frogs will probably not bother you there.
I would recommend avoiding Petrus until you've finished most of the others off. That way at the end you have only him to deal with. Run away / teleport him / teleport yourself when necessary.
Then when it's just you vs. Petrus, leave some traps in his path and hopefully they'll hurt him. Also, drop shitty gear in his path and he might actually exchange it for his, I've seen him do that. Use as many strikes/fireballs against him as possible, and also make sure he's slowed and you're as fast as possible. Then just hit and run, if he hits you even once it will probably hurt a lot; at that point teleport away and don't take any risks. Also, now that the other enemies have been cleared, you should be able to telecontrol to an area where there are none around so that you can leave the city until you've healed, then return.
I don't think you have to apply it to the corpse Chao. The only reason I say that is that I've encountered the repair/corpse bug before and I'm 100% sure i've never tried to repair a corpse