Actually, what if (spoilers)

Bishop actually was someone trying to get the game to continue in the mainstream, and the ghost was actually just a "ghost in the machine" either purposefully placed there or by accident. All unreturned people choose Class Real after completing their mission of assassinating players from Class Real. The real stigma that makes this game illegal in the real world (sepia world) is that people get unreturned which is believed that their brains are fried when in reality they are just chilling in Class Real. The only way for the people running the game to eliminate the ghost is to have zero real people in Class Real. Therefore, they keep sending people into Real with hopes that they will eliminate the player in there and then returning. However, their real problem is that every player Bishop has sent into Class Real has decided to stay there. Murphy was one of the last, but Ash decided to stay thus ensuring that Real will keep going. That is the reason the ghost smiled; Ash deciding to stay meant that the ghost world would continue until the next player is sent in to accomplish the mission of helping to defrag the system. They cannot simply defrag the sourcecode of this Class while a living human brain is inside it because the human brain much "bigger" and more complex than any supercomputer could possibly be. We can easily patch games these days because everyone plays by the rules of the game. With the human mind there is no limit to the complexities. This is the reason I believe they may have needed to rid Real of all human mind before they could eliminate the ghost.