I bet you can get away with elemental and do just fine, likely the amount healed will be offset by having the mobs drop just that much faster.

I would swap out a mage for some other class, just for the character depth. Perhaps a warlock or shadow priest, there isn't much synergy with having an extra mage and the twitch is pretty minimal with some of the rotations in use right now.

That said, its going to get you through heroics easily.