One of the difficulties of videogame novels is the "characters can't die" problem (basically the Seinfeld "no hugging, no learning mantra where the characters need to end where they began). If you use characters from the games, the novelist runs into trouble as the characters are on a strict story line. For example, in the Star Wars novels that take place between movies, many characters need to make it through the books largely unchanged because they appear in the later movies. In the sequels to big games the developer doesn't want to explain that one of the characters died, another switched sides and two of them got married because of a novel that took place between the games. So pretty much most of the interesting story lines break the canon.
