It's early in a new game. So far against the druids I'm running at 50%, but luckily there are 5 in the province (I think there's always 5 blood druids). In the assassinations, the blood druids do brilliant things like cast "Sabbath Master" and "Sabbath Slave" (the same guy). If he summoned Imps instead, I'd be toast!
Anyway, the failures are no so bad, because the blood druids have a nice item each, and I get that as a consolation prize if I have to fry them with lightning bolts because of a failed seduction.