Wasn't Pact of the Undying one made with an undying force, like extremely old lichs, and those who have found a way to escape death? Those still to me fit the mold of a 'Warlock' far more then 'celestials'. I hate class banning, or class changing. But a Celestial Warlock may be the first I...
I don't know how much clearer it could be. You hit before you damage. So it is based on your Current HP at the time of this Hit. Or transversely, your DM can make the decision. Sorry, 4th Edition held people's hands far to much for my liking.