In DFRPG, you have the 7 laws of magic, which if you break you automatically have to add it as a power. Lets say we have a focused sourcerer who's used 6 of their 7 refresh, and they break one of the laws. Do they add the power and drop to 0 refresh, or are they forced to give up something to keep them above 0?
From Your Story, page 232:
A Lawbreaker ability is a supernatural power (page 158) that reduces your refresh by one—you should sit up and take notice here. (Remember, if a character’s refresh ever drops to zero or below, he stops being a viable PC. He loses his free will, becoming a creature subservient to his nature, always acting in accordance with what he is rather than who he could be. Break enough of the Laws of Magic, and the cost of these abilities will eat you alive.)
So strictly by the rules, they add the power, drop to 0 refresh, and become an NPC. But that's no fun, IMO. The PCs know this possibility, so if you warn them, and they do it, then it's a big deal. So play it as such. There are a few options that I can think of readily.
- Don't let the other PCs know. Let the PC continue to play (the session at least), but your compels are more powerful than usual, representing the character losing control. They gain fewer Fate Points than normal, representing the loss of free will. This gives them the ability to fight for their character, and you the ability to have a little drama.
- Tie part of their magic to the law-breaking. If they broke it with Evocation, then one of their elements are tied irrevocably to the magic-breaking, and if they use it, something bad happens.
And those are only off the top of my head. In the end, I think that anything that causes a PC to leave the game should be played up for drama, and not used lightly, no matter what the rules say.
I'd say they drop to Zero Refresh and become an NPC. They chose to become a monster. This is why having a bigger buffer of Fate Points is important. That said, it would be a short-term problem as a Warden would likely show up and behead the NPC for breaking a law thus making the fact they're an NPC now a moot point.
Rule of Thumb: Don't break the Laws of Magic if it takes your PC in to the Zero Refresh range if you want your Character to live long. Having refresh left to you means you can be redeemed, going to zero refresh means you crossed the line into being a monster.