Loss of Compass AND GPS


Currently flying 4.2.2 on a Cube blue. I am trying to figure out how the airplane will respond to a combined loss of both Compass and GPS information while in autonomous flight (airspeed still functional).

I’ve been running a bunch of SITL sim sessions, and simulating loss of compass and GPS. In the sim, the airplane continues to navigate the mission without error. Is this a “sim-ism” artifact? I’m inclined to believe that a loss of position data from GPS and compass will lead to a quick degradation of position solution and eventual crash? Or will the airplane revert to using airspeed and IMU data to dead reckon via inertial navigation?

Edit: also, is there a way to enable an RTL upon loss of GPS without resorting to Advanced Failsafe features? From what I can tell, EKF Failsafe is only available for Copters/Quads…?