I have accepted an airplane with an item MEL'd, read the requirements to the FO with him agreeing, flew the flight and found out later we were not legal. No jeopardy that time but after that I always handed the log book to the FO to concure we were good to go.
It sounds like this accident will also prove the MEL was not used as intended by Boeing. If the heater failed to heat they were legal. If it heated on the ground and they disconnected it, that was not the intent of the MEL.
The judge charging them with a homicide seems a bit extreme.