Dullahan's insta death doesn't exactly have the highest accuracies from the videos I've seen so far. Eros is a surefire failsafe in case the insta death does happen, then again you have 3 turns to cleanse it or kill before the insta death actually activates.
Also... I'm assuming you worry about heals because of the stun trigger? Umm remember you have 2 big hel pots, assuming you don't spend them before boss.