Why don't we just say we chucked the stone out the window or something and Martin is dead? That's what is actually in character. None of the vampires were ever "impressed" by him. Nobody wanted the stone. He had nothing to barter with except the potential to mess up the castle floor, which we would have endured just to kill him. 

So, the stone got destroyed, Akje. Do you have any scenario where Martin wouldn't have then been killed or enthralled by Bedivere after that? Which do you prefer? Cuz that's what's happening.