I read in this forum and there are cases complaining the IMU and Compass error which result in fly-away. Will it be good if a) for Compass error - Spark tries self-recovery like stay hoovering and reinitialise compass unit then make a rotation around itself and if failed 3 times just entered atti wait for rc command or slowly decending to safe area, b) for IMU error - just decending to safe area slowly.
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If the error is from hardware malfunctioning tempolary, we may not lost our Spark or do not harm anyone. The Spark has ability to identify objects so it should be able to identify area without people, cars and not water. It can also use the camera to try to keep attitude stable
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If the error is from software then initiate an interrupt to run a safeguard that perform the robust function.
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Just an idea for future firmware

That could be an interesting idea to retrieve a tempoaray degraded calibration that way.

Other idea would be to put the Spake on a "squared" flight pattern with pretty high flight sppeds so it get a rather precise course over ground heading indication from GPS.
GPS positions are not so accurate, but velocities are more precise so it could be able to find it's way home.
Even if heading from a non gyrocompassing IMU like there are in our UAVs can not find North themselves without help from a magnetic compass or GPS, losing the magnetic compass should not result in fly awayw when doing a RTH.

It should be a degraded RTH but Spark with it's current sensors and well designed flight logics should have some level of robustness to loosing the compass.

There should not be flyaways when GPS is not lost. (If GPS is lost, the issue is then different)