Julie Plec doesn't intend to kill off Bonnie even if Kat leaves. she stated that Kat could stay as long as she wanted or come back if she wanted. So Bonnie will most likely just be written as going off some place.

Loved all the Bonnie and Damon scenes, but the last scene where she confronts him was simply heartbreaking and had me in tears. So great acting from Kat..