Well this is just a hypothetical question brought on by a friend of mine
telling me he made it 20 minutes after his alternator died on his Lumina...
I was thinking, with no spark plugs and much less of an electrical load, how
long would a diesel engine run without any alternator?

Seems to me only the ECU would need power (no electric fuel pumps on a
diesel right?), lights could be disabled by switching them off and pulling
the parking brake up far enough to activate the DTRL shutoff - but not
enough to apply the parking brake.