If you either go to airplane mode each night, you might want to try out some automating app like Timeriffic (free) or Tasker (~EUR 5) which could switch on airplane mode at night, and automatically switch it off in the morning. This way you do not get stuck with a grayed-out menu item -- and in case you do and need to get out of it, you may just need to play with some profile in this app.
Another alternative would be using some toggle-switcher (e.g. Elixier or Power Toggles), which provide you with widgets to switch airplane mode and more.
Also, on many Android devices, there's a pre-installed widget available which usually also includes airplane mode -- mostly called something like "Power Widget" or "Energy Widget"; just check the lists of widgets available to be added on your device.