Would it be productive for Redcloak to cast True Resurrection on Xykon to weaken him? It appears that Xykon wouldn't need to be present for it, so he might not be aware that it was being cast until it was too late. I suppose that the same constraint of "the soul must be willing" applies as for Raise Dead.
That is, if the spell were available in Stickworld, which we've been told is not the case.
EDIT:
Like the Watch in Ankh-Morpork, under Commander (etc.) Vimes?