I have only faced two death lords so far. The first one used disarm once, which I didn't even have back then, and I was all baffled for a moment, then wasted the fool with lots of spells (I guess that might explain why he only used it once). The second one didn't actually use disarm at all but unrelenting force. I thought my character died when I got a third person anim of him falling down stairs, unresponsive. But then I regained control and killed the fool. The draugr was more than half-dead anyway being a pincushion of arrows.