Without buffs wiping on death, dying is pretty much just an ap tax, plus the annoyance of spending another second to click on heal, then click on physical or magic to resume attacking. It is an annoyance that can add up over tens of minutes though :/

Oh, yea, and how these bosses sometimes do percentage damage is really annoying. Using Energy Drain (from... one of the SSRs, I don't remember which; maybe Satan?) to eventually get my rear from 93k hp to 930k really ought to be more impactful than it actually is.