I know that there has been quite a bit of discussion about the whereabouts of the Captain at the time of the incident. Yet it has always been assumed/agreed that there were no less than two alert crew in the cockpit as per regulations.
I was just reading a UK CHIRP report:
http://www.chirp.co.uk/Downloads/ATFB/ATFB90.pdf (page 12), about a worrying incident.
The flight concerned had four pilots, two went to the bunks for sleep.
The cabin crew were then instructed NOT to contact the cockpit at all, as a third pilot was taking a rest there!
So there was only one fully alert(?) pilot for at least some of that flight. The other, sleeping(?), pilot probably not much use should a sudden crisis arise.
I am not suggesting that this happened in this instance, but it does seem to rather diminish the discussions of assumed crewing rules and practices in this thread.