While we may never actually know what might happen in a given theoretical situation, here's how I kind of picture this playing out:
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Tarquin: *gives his little speech*
Roy: Hmm, you make an excellent point, let me think about this for a second. Let's see, since you fall just below Xykon and just above my father on the list of people I most want to see burn in hell and you've already proven a willingness to aid our enemies, I think we'll just kill you and stuff your body in a bag of holding. Worst case scenario, we buy ourselves some time while your lizard buddy burns the resources to True Resurection you back to the world of the living...provided he can, of course. Then YOU can decided if it's worth your while to hunt us down, or wait for us to come back and get you, again. So in conclusion, my reply is this: Order of the Stick, kick his @$$.