Give me one good reason why you would not use the ferry tank fuel before the in wing normal supply first while you were still in range of a divert on only the main tanks in case of issues with the ferry tanks?.
It would be very doubtfull I would do that in castostrophic equipment failure (and the autopilot failing doesn't come under that heading). On the other hand putting yourself in a situation with no escape options you would be called an idiot.
There nothing much they can do now the aircraft has gone. They might do some fuel calcs and work out that if he had used the ferry tank first then he would have had discovered the issue within divert range on main tanks. Then a big faa stamp in his log book saying ran out of fuel.
Or they will just take a pilot report and do nothing.