Healers, not required. (EW SPOILERS)

[Packetdancer]

If I remember correctly twice come ruin in delubrum also gave a damage down according to the tooltip on the debuff but I have no idea how much.

Hrm. I don't remember it doing so, but I'll be honest that I'm not absolutely certain of that. I'm mostly certain it didn't in Eden savage -- you got the damage down debuff independently of Twice-Come Ruin if you screwed up a mechanic, I seem to recall -- and I assumed they'd just literally used the same debuff. But like I said, I may be mistaken.

I am like 98% positive that Thrice-Come Ruin in Delubrum savage didn't, but maybe that was only because it didn't have a timer. (I.e., you only got to screw up twice, period, across an entire fight before it just nuked you.)