Nfpa 72 21.4.5 Says loss of voltage to control circuits shall cause a supervisory signal. This intimates that power is always to be available, so circuit is always fail safe hot. When heat detector closes, or fire alarm panel initiates, it need to shunt. Shunt coils by design shunt when power is brought to it, not when it's removed.

NFPA 72 21.4.6 the devices used to initiate shunt shall be monitored for integrity by the fire alarm panel. So if heat detector gets used, or knocked off the wall, panel should read a supervisory closed, or open circuit trouble.