Im a bit confused as to how 'severing his connection' to the staff would help against my attack. I was under the inpression this weapon was in fact his soul. Even severing his connection to it, would it not still be a wholly spiritual construct given shape? I don't imagine this is a polearm infused with his soul, but literally an extention of it. I cant imagine severing it would both rid it of its magical conductiveness and still be able to exercise control over it.
Edit: This is also happening at lightning speed literally, since this ethereal lightning moving through his staff is equivalent to electricity coursing through a metal. On that note, if one were to send an electrical current through a bar of metal, cutting the metal in half would not sever the current. Youd just end up with two electrified bars. Unless youre arguing that you cut off the metal before the current passed through the rest, and that's what I'm getting from the post, I don't see how the technique would work. And that's a huge stretch even by pc standards since it was channeled on contact thus nullifying any form of believable preparation for it.