This raises the question: For whatever reason, poor design, poor maintenance or both, a common point in an a/c has been compromised and the electrical supplies severely downgraded. I am VERY surprised that there is no facility to start an APU, although that would probably not have been 'connectable' as it doubtless was bussed through the same area.
As someone else has said, had this happened further out within the operating area of a large passenger plane, it would probably have been inexplicably lost.
Do we therefore
1) Accept this as the statistically acceptable risk?
OR
2) Ensure that at least a separately powered attitude indicator with sufficient endurance for the operating area is fitted, PLUS a back-up independent nav system as also suggested. A venturi driven AI would also be fine - and cheap. A battery of greater capacity than ?30/45? minutes and located away from the 'danger zone' would help.
With these, gravity drop on the gear (as per the 737) and (presumably) self powered engine tachos, a crew has a more than reasonable chance of getting the a/c down somewhere in one piece. The battery could even be turned off when initial actions are done, the recovery made on the back-ups and the battery used at the end for flaps and gear etc.
Is the cost etc of this justified? Over to the floor.
I should add - kudos to the crew!