Plot hooks are an invitation to engage, not to fly off the handle. Again, engage within reason. If a player throws all reason out of the window because 'it says so on my character sheet', then that's the point where things have already gone wrong. An experienced and confident DM could and would have salvaged the situation but let's not forget it was the player first who 'had issues', the DM second, although I don't really see much point in playing the blame game here. Regrettable errors were made on all sides that lead to the implosion of a potentially great campaign.
Also, just for the sake of preventing unfortunate incidents in the future, it's a completely unwarranted assumption that slavers would never employ deadly force, especially when attacked.
@Galithar: I believe we are in agreement with only semantic issues slightly muddying the waters ('wrong', 'player vs. PC'). I agree with how that tasty crunchy leg was handled. Then again, having a fluffy wolf carry a treat around is slightly different from trying to axe a slaver in the face, right? ;)