In an attempt to reform your bubble, think of it this way.
The Strega was, to my understanding, a force of reality, like the weaver. It was her job to destroy reality when it got too corrupt and whatnot so the Weaver could start again.
Saying we killed the Strega is like saying "Yeah, we killed night-time."
But at any rate, we destroyed her physical form. Juding from what she told me in a moment of Cade's-charm induced weakness, it's gonna take her a LONG time to reach a power level where she can even think about influencing reality again.
So, for the rest of YOUR lifetime, yeah, the Strega is dead.
Shame too, because, for a being bent on destroying all of reality, she was fine....
Cade~