On Sun, 3 Jul 2016 09:32:32 +0200, Mike Wey wrote:

For windows you could set an on delete handler that hides the window,
return true so it stops processing other handlers, so the window doesn't
get destroyed anyway.

yourWindow.addOnDelete(bool delegate(Event e, Widget w) {
	w.hide();
	return true;
});

That did it. Thanks a bunch!