If the drone can transmit information (about incoming radar signals etc.) back to base, right up to the moment of the kill, it can be a great success.

One of the first uses of drone warfare was the Bekaa Valley missile crisis of 1981. The Syrians had set up SAM 6 missile defenses in Lebanon's Bekaa Valley. The IDF sent them decoy drones to trigger them, but the missiles would overshoot the slow moving glorified model airplanes of the day. That was a great expense to the Syrians, but the operation was not a success until the SAM-6s finally downed a drone.

The following year, Israel invaded Lebanon. They had effective countermeasures for SAMs based on information from the downed drone.