By the time they had discovered who had taken the Vampyr book it was by far to late to reverse what had been written in it. All of the Slayers were dead and only Willow's legendary powers prevented the Book from killing her as well. And the world was being ripped apart by the contradictory things that had been written. The world was truly ending this time and there was nothing Xander could do to stop it. No amount of violence could erase what had been written in the blank Vampyr book