That's probably fine at this stage because due to end of expansion itemization healers effectively have unlimited mana supplies. At the beginning of an expansion, however, it's actually bad practice to waste all your mana on the guy standing in the fire. You're better off letting him die so that you can conserve your mana for the competent players. Same applies to tanking. It's better to let the guy who pulled die so that you can keep yourself alive for the other players. I've seen many attempted troll facepulls fail because everyone had the presence of mind to let the idiot who was doing them die by himself. When no one else hits the mob it quickly drops aggro and resets.