Did Mag and HKM. Mag was a one-shot. HKM was a twoshot when I realised that killing HKM is enough.
I just put my guys against the wall, pull the lot and burn down the priest with 4 earth elementals running around. Once he's dead, I just kill HKM and win the fight. Even if you die, he'll still stay dead and you can move on to Gruul.