I got to the second sub-boss, the Seer, slowly ticking him down with DoTs while my meleers hacked through his protective rows. He's down to the last few hits, but then wipes three of my party members and leaves my Hellion on Death's Door with a debuff. He's two hits away but without healing she won't make it. Fuck it, I hit him with the glaive, have a freak crit and kill him. I practically jump for joy, then I remember those other three party members are permadead and there's no save scumming to try for a better result.
For her success, I rewarded my Hellion with a week of flagellation to reduce stress. Luckily I think I can dive right back in because my Crusader just got his syphilis cured.
The ups and downs are very Dark Souls.