The "event structure" can capture events for "this VI" that include "panel close". If you are using an event structure to look for the push of the Done button, just add another event that will catch the panel close as well (you can even configure the stucture to not pass on the close event). If you are not using the event structure to watch for the done button, perhaps you should. If you cannot use it in the same loop, you can put it in a parallel loop and use any of several signaling mechanisms to communicate between the loops.