These termination terms have to be realistic in the knowledge that you can’t prevent someone from following their own profession and skillset. If, however, he is still under contract and working out his notice, which would have been included in his contract of employment, then he is on payroll...
I struggle to understand how anyone with an ounce of decency in their bodies would want to work for that regime. A decision to move there would, in my book, be a show of true colours and they won’t be blue and white.