Leaving Storybrooke and leaving the real world are two very different things. I was saying (and I didn’t explain it quite right) that if she jumped to another realm the fail safe would activate.
I have toyed around with the idea of it being other things. But it almost has to be tied to her leaving otherwise it could backfire on her and she would die as well, or if you are right(and I think that you are) that she could leave Storybrooke, at the very least be stuck in the real world by herself.