How badly can your neck/spine have to be to require surgery?

Varies. In general, there are two reasons surgery is considered. First, if there is a present or impending problem that if not addressed surgically will lead to a neurological or medical problem. For example, there are some people at risk for paralysis unless they have surgery. Second is if the spinal condition that causes symptoms that have failed nonoperative care, such as in chronic back pain.
Depends. Depends on your particular case you need to discuss this with your doctor.