That's probably not possible. When the process loses the connection with the X server, it normally cleans up all of its internal data associated with the GUI. It doesn't have to, but that requires significant effort on the part of the programmer (they would have to work around the standard libraries). Most programs don't offer an option to open a new GUI window if the existing one has been closed, either.
If you fear that your connection is unstable, you can use xpra as a proxy between the application and the X server. Xpra creates a layer of insulation between the application and the server that allows the application to move from one server to another; it does for GUI applications what Screen does for text mode applications. Xpra has to be used when starting the application however; afterwards it's too late.