WFRP Slayers and Players
I read in a comment thread about Slayers seeking death that someone stated, "There was a discussion about this some time ago...He made a sacred vow to [atone] by being on the front line so that people more worthy than him can stay out of harm. He is an individual living a dangerous life to protect his race."
What we learn from the novels is that the Slayer is seeking a glorious death, one that will wipe his shame clean and return the family's honor. The Slayer doesn't want to die to a plague or a building randomly falling on his head. He wants to go out against a deadly foe, put up a respectable fight, and go down honorably.
As far as the gaming aspect of this, I don't think it's too cruel to keep the Slayer alive, if that is also the hope/expectation of the player. It seems like there needs to be a bit more collusion between the GM and player on this one. From what I read, that's the mark of a good GM anyway, talking with the players about their wants/desires/expectations and running the game accordingly.
On the other hand, the player should in no way get upset if the GM gives the Slayer a glorious death. That is the goal of the career. The player should know this before agreeing to take on the character.