How keep player connection on disconnect

The player is connected to the server through the velocity proxy, but the server turns off and the player kicks, how can I keep the player connection to the proxy until the server is turned on. Perhaps this is a trivial question, but I’m new to minecraft proxy servers.

This is simply not possible, you could however use a second server for when you take one server down, the users will be forced into the second server like the hub or lobby.