I recently did something similliar for a friend with a wire EDM machine, when the EDM wire broke, the machine stopped.
What I did was wire an indicator light to the output of the cooling pump contactor. The cooling pump shuts off when the machine stops. I wired a 220 volt relay to the output of the contactor for the pump. Pump running, contacts close turning on green light, pump stopped relay de-energized and red light comes on through normally closed contacts on the relay. Light is powered from a 120v outlet next to machine. The light fixture itself is an old traffic light mounted on outside wall of shop that the owner can see from his house.