What is your use case for such a thing? Also, what do you mean by 'server has regained control'.
There are two ways for the server to regain control. The first is by manually locking control on the VI. This is done so the operator on the server can use the VI without control being taken by a random client. You manually unlock it when you are done. It wouldn't make sense to make this unlock automatically because then a client could interrupt you while you interact with the VI on the server.
The second way is if the control timeout is set. In this case unlocking control is not necessary because control is automatically transferred to the next client in line. It wouldn't be possible to unlock control in this case because the server never has it.
If you want to do these things programmatically there is a VI server method on the VI class: 'Remote Panel.Close Connection To Client' or 'Lock Control', etc. You could have another VI monitoring your remote panel client connections and locking/unlocking control of them as you would like.
Does this answer your question? I would like to better understand what exactly you need to do.
Nathan
