Name 88 will want to kill me for saying this, but you can kill off Quinn... But...
It would hijack the entire game. She is such an important character, that unless it's a suicide, accidental or the murderer is caught in the act, the mystery surrounding her death would become the game. She has connections to a lot of people and the most important groups in B&R, everyone could be a suspect in this situation, and motives all around because of how she likes to mess with people. Sometimes you cross the wrong person.
That would be a crazy twist, BUT... Like i said, it would hijack the game. After that it won't be a game about college shenanigans, but a investigative VN with porn in it. I bet most people would be pretty pissed and frustated with this, not to mention Quinn's fans that would be up in arms.