What I'm driving at is, they were holding first at 8000, then at FL150. Is it possible the increase in fuel burn at that altitude compared to cruise was high enough to eat up the 2 hours? Is it possible the aircraft indeed ran out of fuel during the GA, stalled severely and impacted the ground while trying to recover?
The crew will actively monitor the fuel situation and not let it get anywhere near fuel exhaustion. The FMC is a good help and gives you hrs+min available for holding before you need to divert, based on the diversion fuel you've entered in the FMC. Either it uses current fuel flow or predicted fuel flow at best holding speed at present altitude. Either way, it's good enough.