At what point does the games story become separated from the game itself. Some games are used as mediums to tell stories in the same vein as movies and books. Would questions about the plot be more fitting in Scifi.SE. What about a story that expands past the games? If a book is written about a game world, does the contents of that book fall under this site, or another?
I think questions about plot would be more fitting elsewhere because that starts to get into the area of discussion and debate. The few questions I have seen on Gaming in this area have been in and around the area of requests for videos of the ending or some other part of the game where the person missed out on it in one way or another and the game does not provide an easy way to view it again.
As for the books, I would have to say that they are completely off topic for this site in regards to its contents. The reason being that what about books that came before a game? Take Parasite Eve for example. The game has had a noticeable following but I have also found out that quite a few people do not know it was based upon a book that came before it. I can not see any question that would come from the book in relationship to the game that would not be discussion oriented.
At the end of the day, I think both points in the question posed above would almost always resolve around discussion oriented answers as opposed to the more Q/A aspect that this version of SE tries to adhere to.
My two cents is that as long as the video game is basis for the plot of the story (ie the game or games is directly tied to the book or comic or what have you) than I would say it is on-topic, so long as the question ties back to the game. Note, that that does not mean that I would consider all video game novels on topic. For a distinction, I'm going to turn to books I've read which relate to the halo series.
I would say that The Fall of Reach, which is a prequel to Halo, is on topic. It features the main character, is directly tied to the story in the game, and is closely related to the plot. However, I would not consider The Ghosts of Onyx on-topic. While it does take place in the Halo universe, it isn't directly tied to any (current) games in the series. There is speculation it might tie into Halo 4, but that is yet to be seen (and speculation is off-topic).
Now, if the question is strictly about the book or the contents of the book, and not how it relates to the game or plot of the series, I would say it is off-topic. But I could see questions about how the book ties into the game or visa-verse being on-topic.