Probably nothing since there is no voltage going through the circuit (at least NACs). Well there is, but it’s about 2 volts which is checking supervision. 2 volts will do absolutely nothing if shorted. Even if it was energized, 24 volts is such a small amount of power that you might get a small spark but very small, potentially unnoticeable.
For addressable loops (and IDNAC for Simplex) there is always power in the line, but the communication happens as small drops in voltage. The circuit is pulled to Vdd and then the ones and zeros are represented as drops in current. The devices have a capacitor large enough to power the microchip on board to receive the transmission. Thats a very simple explanation, there’s a lot more going on, but that’s the basic part of it. Usually the circuits are brought to 24 volts. Same thing applies here, 24 volts is very little and possibility of shock is small.
TL;DR probably nothing if anything at all.