Why is it forbidden to cast the Sacrifice spell (second level of Necromancer's Tears) on a vampire? And does anyone even manage to develop the second level of Necromancer's Tears?
Oh, they definitely manage. People get the second level of Tears/Blood (there are ways to get it even on the first week) by the second week.
The vampire goes into defense mode, and its "out of time" ability makes the entire army almost invulnerable.