40&80:
From your post I digest the following:
Hypothesis is that touble with one engine leads to a set of actions in the cockpit that ends up with the "good engine" being inadvertently secured rather than the bad one. As I have seen a similar thing happen IRL, early 90's mishap in the Navy, and watched more than one crew make that error in sims that I ran back in the day, it will be interesting to see if the facts as found align with your estimate.
There is also a chance of various fuel flow malfunctions arriving at once, but I'd need to take a look at the MD 80 fuel system schematic to try and figure out how flow goes awry ... presuming that there is usable fuel to move about in the first place.
Hope the FDR info becomes available in due course.