The most likely theory, in my mnd, is that the aircraft crashed somewhere at sea. But where? And what about the fuel sheen that it would have left? That should have been visible for days. But unfortunately, it was days before ANYBODY starting seriously looking for the aircraft.
Seven years on and we still can't locate the AFR A330 that crashed into the Atlantic and a search was almost instantaneous for this one. You can't hide a 727 these days no matter how hard you try, so to my way of thinking, it did crash (probably at sea).