Necropolis – “Dawn from All Sides” [Campaign 2, Mission 3]

Here's the situation. I started playing, went to Ludmila, took the quest, defeated Sharka, although the hero kept dying on auto-battle. I lost about 30 skeletons and 50 ghouls, but I still have a hundred ghosts, 20 liches, a hundred skeletons, and 50 ghouls, plus a weaver and 30 vampires in the town. Then, out of nowhere, an evil Necromancer of level 21 appears from the sea and starts casting explosion and chain lightning. I lost without a chance. I think I rebuilt Sharka's town, but there was no new weekly replenishment there. Do I have to start over? I'm playing on normal difficulty, and I didn't expect to have so many problems with this mission.