Desk pilot
Im glad you spotted the hydraulic leak.
What makes you sure there would have been a complete hydraulic failure? Possible yes, definate maybe not, impossible to tell without knowing the how "leaky it was. Presumably it wasnt showing up as a warning, as it wasnt yet one. I would guess the computer would fly the aircraft after hydraulics failure in the same way that you would do, using the emergency procedure.
What makes you think that a single failed AHRS (or ADAHRS) in a dual or triple unit system would be a problem to a computer, or its back up?
Do you have any quantitive evidence of how often computers go wrong?