The Taser has been fired. It cannot be fired again without a new cartridge.
Slager is well aware that the Taser has been fired.
Even if Scott had the Taser, he could only use it in contact mode, as a regular Taser.
Scott was no more dangerous than any other person with a personal Taser.
The darts are fired once but pulling the trigger can give multiple jolts. The Tasers the PD and the SO carry here carry two cartridges, one in the fire position and one in the grip. If the wires come in contact with skin they can also deliver a jolt.