one news story hinted at some cracking around the base of the antenna arraw, which may have failed in this case, causing the communications blackout.

plausible (also would explain the course change if that's what happened) but wouldn't explain the disappearance unless something else happened to incapacitate the crew/pax.

i suspect that if crew loses the antennae, but were otherwise unharmed, they could still manage to find a runway to set down.

so, were possibly looking at:

something that incapacitated the crew as well as the airframe, but
wasn't instantaneously catastrophic (no debris field in flight path)
no "adios m-f'er" and no transponder, so not likely a human act
no crew or computer awareness of problems before last communication

was there any weather that night? maybe lightning strike? meteor hit?
ground /air to air missile?
front fell off?