There really isn't any way to determine if the stuff is usable or not without trying. It's certainly dangerous. Destroying the very modest stocks of VX in the U.S. took years and there were accidents even with what were considered adequate safety precautions. This place is far worse. Leaking containers, half-filled munitions - the reason it hasn't been destroyed is that the project would be more difficult, dangerous, and expensive than simply leaving it there.
Until now. Because there will be somebody stupid enough to suit up and go in there for Allah and see if there's something he can drag out. For rational people it would be easier to manufacture Sarin for themselves. These guys aren't rational people.