My $0.02...
This is ignition related, the biggest clue was the loss of Tach signal... and the instant shut off.
I always use the way the car died as a good clue... a slow die off with spluttering and a bit of surging is loss of fuel, and an instant switch-off most likely ignition related.
If it was FPR the electrical side of the engine would have read the tach signal, as the ignition would have not "seen" any loss of fuel pressure or fuel. and the Tach would have just followed engine speed back to stall.
I am calling it ignition related.

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2009 Mercedes ML320 Bluetec