Recovery after it's lost power or whatever requires a very accurate knowledge of the plane's exact geographic position (GPS), attitude, and heading relative to true North. That's easy on the ground, more or less. In the air it could be more than a slight bit difficult, especially when we get some vibration.
Given that ACARS didn't indicate a power supply loss, that scenario does not seem to fit this case, but ... to better understand recovery or lost capability ... if you had a power loss / or interruption (part of why there are 3 (do I have that right) in a given aircraft ???) ... then, not only do you need to reset location and direction, you have to establish wings level, nose pitch X, (zero, I assume) to re-establish correct attitude sensing from which the gyro can reference.
That is similar to "recaging" a gyroscopic Attitude Indicator if it has "tumbled" in flight, though from your description, a bit more complex.