D7.11 FP: .... The total FP of an OVR is halved if the vehicle becomes Immobile or destroyed before it can resolve its OVR.....
I would say the FP is halved and the result is figured normally. CC reaction fire would be an option for the OVR target. I would also suspect that the remainders of this would be marked with a CC counter (that part I am not sure about). -- jim