To defeat Necropolis or Haven with the Inferno faction in the sixth installment, I think you need to know the tactics and strategy, as well as the hero's progression path...
There's probably a chance, but only if the game lasts more than two weeks, on a large map. Otherwise, on a medium-hard difficulty level, Haven (mage + priestesses + archers + spearmen) or Necromancer (mage + ghosts + skeletons) will easily defeat Inferno.
