Long post. TL:DR
Nayash and Veragwen atacks once each, nayash sees the others attack, nayash avoids the mob, sees hoodiedude, who she thinks is Illurath, the guy she's after, and rushes out of town to chase him down, as she realizes taht even if it isn't him, killing the necromancer is the only real way to ensure that the dead stays dead.
Shes unaware that most of the town is dead.