20kg Hexacopter in flight motor failure

No. Only the command signal to the ESC (RCout) and in cases with ESC telemetry Motor RPM. But even this RPM is not a direct measurment.

When the vibration levels exceed the full scale capability of the accelerometers.

This is the better of the 2 IMU’s. It’s terrible.

The Z-axis needs to be lowered to where the X and Y are.

That’s always a hot topic. Foam or a isolation mount perhaps but getting at the root cause is the best place to start. Standard stuff; balanced props, cables not tight to the Flight Controller, Nothing loose and moving around, etc. Or it could just be an overly compliant frame.