In this case, however, I can't imagine a situation where a small fire causes enough damage to render all communication equipment useless, incapacitates the crew/passengers, but doesn't cause the plane to crash for another 6 hours.
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How is that any less likely from someone overtaking the cockpit, without a single communication/mayday back to ATC? Unless both pilots were complicit, I don't see a scenario where nothing is communicated other than All right, good night.