However, one question arose to me: if the player would have his character kill the warlock, wouldn't that mean he'd be a Lawbreaker?
Yes, it would have given the PC Lawbreaker. The thing is, I doubt any of the other PCs would have reported it so it was just a question about the guilt of killing another human being. And no, I might not have been entirely fair making the choice "save the entire group at cost to your PC OR endanger the entire group" - but the PC had put everything he had behind his attack. All his FATE points for one last shot at the departing enemy. He wasn't pulling any punches and seven stress points implies an Epic level of damage - and that was after the Warlock did everything he could to protect himself.
With that much damage, onto a guy who had already taken 2 mild, 1 moderate, 1 severe, and had only one stress (the first box) unchecked I think "He's dead" is an acceptable ruling.
That, and I wanted the players to feel in control. If they pound their hardest on the Bad Guy and the Bad Guy gets away then it takes something away from them. This way they decided (because while there was one player making the decision the event table talked about it) if the Bad Guy could run or not...
Interestingly enough, the idea of Lawbreaker wasn't raised until afterwards. As in "Hey, if I had killed him would I have to take lawbreaker" being asked after the decision. (Answer "You mean if you had killed him with magic, would you become a lawbreaker for killing someone with magic?"). Instead it was the player's character concept that decided. He's based around the idea of being a comic book inspired wizard (some of his resources are constantly devoted to maintaining his growing comic collection) and superheroes don't kill.
But on the other hand, after they decided they pointed out that he had bled so they should be able to find his blood - meaning that after resting for a scene (eating the pizzas they ordered) they'll be ready to track him down and handle him - hopefully before he can counterattack them.
So while the choice might not have been completely fair and the PCs saw an angle that I hadn't thought of, the group loved being able to choose. I'm going to try to do things like this in the future.
Richard