Most of the time, someone who lost their wolf spirit wouldn't be as lively as Zander right now. They would die eventually.
Your wolf spirit was akin to your life force, once it was gone, you wouldn't have any desire to live and eventually, your body would follow.
However, it was not the case with Zander and the only explanation that Dawn could get was; something happened ten years ago when they were eighteen, the moment where Zander met with his destined mate and she died. That was the same time when Zander lost his wolf spirit and was unable to shift.
Zenith didn't give her any detail about the event, but from the way he said this story, Dawn had a feeling that he didn't want her to pry. He was not ready to tell her about what happened in that eventful night and she stopped herself from asking.