One thing to consider is that Jerry is so respected within the organization that if he were fired, he'd probably be allowed to resign.
I think that's probably what happened.
Possibly, I doubt he would join another team now anyway. The man is 68 years old and being a head coach is a stress on your mental health and family. He might not have a ring but anyone who knows an ounce of basketball will know how great he was/is as a coach.