Killing the engine while racing would probably be more hazardous than letting it go crazy. Our brakes and steering are controlled by the engine, and if the converter remains locked it will "upset" the vehicle, shifting the weight forward, which can be a handful if you have soft racing tires on the back.
Runaway diesels are problem regardless of whether you are racing or not. The CO2 extinguishers that are at most tracks will kill the engine regardless.
Another factor to consider is that many of these guys are using nitrous. A airshutoff will not stop the engine if the air is coming from a bottle. Nitrous solenoid sticks, turbo blows as a side effect, and you have a runaway until the bottle is empty. Except a normal runaway is "low power" because normally the boost is gone when the turbo shaft breaks, a nitrous runaway is a "boosted" runaway.
Runaway diesels are problem regardless of whether you are racing or not. The CO2 extinguishers that are at most tracks will kill the engine regardless.
Another factor to consider is that many of these guys are using nitrous. A airshutoff will not stop the engine if the air is coming from a bottle. Nitrous solenoid sticks, turbo blows as a side effect, and you have a runaway until the bottle is empty. Except a normal runaway is "low power" because normally the boost is gone when the turbo shaft breaks, a nitrous runaway is a "boosted" runaway.