TH you are correct about failure of power plant generally not being an issue (so long as the engine is not lost from the airframe of course). An aircraft like the Stemme could literally glide almost to the horizon unpowered in still air.
Most likely either damage to control circuits resulting from engine calamity as jokova said or smoke/fume/heat as engine fire, which would not easily be directly observed in early stages, consumed airframe materials. Damn shame.