SLFJB- not sure what you mean about turning the Comms off when away from the home airport. I've never heard of that before. And napping down the back presumes three crew and no bunks.
At my old airline, three crew kicked in at about 8:30 flight time and 9+ for a daytime report. The blanket FAA 8 hr thing does not apply everywhere and I don't know what kind of FTL's Malaysia use.
I would hope that we wouldn't sleep off the flight deck leaving only one pilot alone up there. It sort of defeats the purpose of having two pilots, non? Rather than getting away with an emergency, I would think it more likely that the cabin crew or a savvy pax would complain to management and you'd have an interesting time explaining yourself.