The first was that I was in a Trial Roulette and got Titan HM about two nights ago. Other healer was Astrologian, and I mention this only because I don't really know what their healing capabilities are like. At some point after the second set of outer rings collapsed, the tanks lost aggro and couldn't regain it before Titan knocked me out. I was revived, but because of that, I would spend the rest of the fight with low MP, even with casting Shroud of Saints immediately. Tanks were getting wrecked. Party members were telling me to esuna those freely broken out of Gaol, and everyone was getting hit by AoEs. I decided to go with the AoE healing route. It didn't work out very well, judging from the amount of deaths in the party. We still cleared that attempt, but I still feel really bad about it.

In that situation, what should I have done, with my limited MP?

-> Heal tanks only
-> AoE healing anyway
-> Immediately revive anyone that dies
-> Esuna away the Determination Down debuff