Neither.
More like "Sure, you've got my life below zero, but I have Lich's Mastery. Oh, now I need to exile a bunch of things because of the damage I took? And if I take that much damage again, which I will next turn, I'll have to exile everything (including Lich's Mastery itself) and therefore lose the game? I think I'll exile it now, instead, and the trigger won't kill me because of my Gideon of the Trials. What's that? Gideon's gone? Good thing my life's above zero again!" et cetera.
The opponent is doing exactly what they were already planning to do, but I survive it.