This can only work if all the pumps are fed by the same voltage and phase. If the pumps are on 2 or three phases (each pump using only one phase), and you break the neutral, the pumps would still have voltage across them. Only if each pump draws the same current would they split up the supply voltages evenly. In any event you wouldn't get shutdown.
If everything is fed by one voltage/phase source, then you could put that contactor on the supply wire, and leave the neutral alone.
