Lonewolf_50, are you familiar with how a l@ser ring inertial reference works? Your remarks suggest you are unfamiliar with it and are extrapolating from physical gyroscopes. I'm sitting here puzzling over many aspects of your comment.
First, how do you cause a l@ser ring Intertial Reference Unit, IRU, to tumble. There is no moving part to tumble. My understanding is that the three rings are bolted down relative to the plane. The planes changes heading, pitch, and yaw are digitally processed to get the actual heading, pitch, and yaw relative to their state when the IRUs were initialized. Then you play with accelerometers (and to a degree the laser signals) to determine your position from integrating your direction of movement relative to the plane and its absolute heading. Then, since its most useful to know "up" relative to the surface under you rather than the tarmac on the airport you left the absolute reading is translated in coordinates to match your current position.
Once calibration is lost you probably cannot regain it in a trustworthy manner until you are on the ground.
And where in the BEA reports does it declare the IRUs themselves all went
unreliable at the same time. This exhausts my imagination trying to figure out how thus could happen short of a total power cut.