Lyman, taking a plane that is not stable, if HAL did something odd, is roughly the same as taking the plane from another pilot who is flying badly or has vertigo. If you fly in multi-crew aircraft, I run with the assumption that the above is one of the tasks that you are required to do, and trained for.
If you are not trained to do that, one wonders "Why not?"
I refer you again to my old refrain: what did he(PF) see? Though the betting money is on all of the AH's working, the PNF did switch sources to a different inertial gyro for one reason or another.
What was that reason?
More than one possible answer, and since they didn't verbalize why that was done, the why is left open to some question. Those who have flown the A330 may be able to offer better estimates that I, so I won't attempt to.
Nothing further.
Out.