Holy nova really does not heal enough and EATS your mana too.

YOur group is a bit different with the pally but it should still work.... mages IAE and Warlocks Hellfire .... priest @ level 30+ Prayer of Healings.

It works - BARELY - with locks, demo specced. The mobs die a bit faster than I die - but without 4 locks 1 priest..... not sure that is a viable strategy or not.

But try it and find out!