What if a cruise worker gets fired during the cruise?

I’d imagine there’d be restrictions just as if someone had committed a crime. It would depend on the severity of the offence. Ideally, you’d want to hand papers to the employee while the ship is in port, preferably at the end of the voyage or have arrangements made to take the employee back to the point of embarkation. It depends if you can trust them enough to continue with their duties until you reach port, or have them assigned to a different set of tasks. Access to their work areas would be secured with a new keycard and the employee could be secured in the room if necessary with room service only. You’d be short staffed while the employee is out of action unless you can ask someone else to work an extra shift or put more time in. It would put more stress on the other employees. They may have to pay a fare out of their salary.