Actually, Aranthir resurrected Erish after Markel was defeated. The campaign for him begins with this, and it talks about the decline and fragmentation of the Necromancer faction. By uniting the Necromancers around the fulfillment of Ash's will, Aranthir gained control of the entire kingdom.
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Didn't Aranthir benefit from this? After all, as everyone knows, Ash turns everything to good use :D This is, of course, a joke, but Aranthir repeats this 10 times for a reason; there's meaning in it. But Markel never saved the empire. If he saved it from anything, it was only from Isabel. :) And he also did a lot of bad things. What about the resurrected Nicholas? What about the hordes of elves he killed on his orders? And he also caused a lot of turmoil in the empire itself. And in general, he wasn't as devoted to Ash as Aranthir was, who, by the way, was called Ash's chosen one. IMO, Markel is the only truly evil character in the 5th game.