It may not be strictly necessary to utterly destroy everything left of New York, but Ilde's rarely (if ever) inclined to contradict Sonja's decisions on anything and if you had a bad break-up with the antichrist (or close enough) then you'd probably have strong feelings about thoroughness, too.

(And let's be honest; Ilde wasn't going to contradict a plan like that. She likes to burn shit down, it's kind of a thing.)

"Corrupted power," she says, almost blithely. "Not right. Feeding on what's left. Vampires are very low on our food chain, if that puts it into some context for you."

That is part of why she's so sanguine about fucking Ivan; the other part is 'Sonja', honestly.