Sleeping??
Guys,
Cut the crap about sleeping and such! Button touch monitors and such do not protect against missing calls by ATC over the radio.
The guys can well have been awake and busy, but have missed radio calls, that's all. Perhaps they have accidentally turned down a radio volume knob.
Could they have realized sooner that the radio was awfully quiet? I bet yes, but perhaps the flight was during a quiet period anyway - don't cargo's often fly opposite the busy time of pax operations?
Launching ready to fly airforce jets is standard practice to clarify such a situation, nothing that any airforce type will get nervous about. Man, how often doesn't it happen that some Cessna pilot does not properly file a flt plan and has to be intercepted for identification?
In short, don't make an elephant out of a mosquito.