Couple fights in WoW spring to mind like Valithra Dreamwalker and Tsulong where healers have to heal the boss on top of healing the group dealing with mob waves. There could also be a boss fight like the grand fate in Churning Mists with DPS damaging the boss while healers heal the NPC fighting it alongside the players.

With how MP and Piety will be in 5.0, those sort of fights might be something interesting to see play out.