Alt+Shift+F12 will never work, since you cannot use any combination that use the Alt key, since the Alt key is reserved to the sim menu.
It's normal GSX won't show in the menu bar if you disable it. You shouldn't disable GSX when you think you have a problem with it. Instead, you should use the "Restart Couatl" option, which is there precisely to restart GSX WITHOUT disabling. Disabling GSX should be done only in case there's conflict with some other add-on.