Well, the problem is that until I beat that (...) Xalabar I cannot follow any further with the main quest...
While searching I found (probably) the same problem, but the thread is in German so it didn't help me much
I suppose (as I understand just basics of German), I should load an old save (in one fourth of the map) or replay the map - let's say, it's not a solution, especially that I don't know how it might help.
I'll continue searching, on the other hand, I'll replay the map. If the bug repeats, I'll deinstall Spellforce and buy Sims 2. Ok, just kidding