That might well have been so, but she gave them a warning at the start of the season. So they could have sent her of to Paris to study or anything, you know like they did to Jackson whom they should have killed off.
Leaving room for her to return.
Or hell, considering all the warning they had, they could have given her a proper send off. If they'd given Crystal the nogitsune storyline instead of wasting it on Stiles, the season would have been a hell of a lot better and at least her death would be more meaningful.