What are the chances to get his probation reinstated if he violated a no contact order and his PO wants to revoke probation?

Ultimately it will be up to the judge. It will depend on a number of factors such as if he has had any prior violations, how well he has done on probation, how long he has been on and how long he has to g. I would suggest retaining an experienced criminal defense attorney in the area that handles probation violations who will be familiar with this particular judge and can make persuasive arguments.

Cannot tell without the details and history. The PO's opinion will have a lot to do with it. Show remorse and compliance. An attorney would be most helpful.