Under normal circumstances, it's obvious that the original writer would be in control of the canon, but what about when the IP-owner is deceased or no longer participating in their industry? This applies to anything requiring writing, be it fiction novels, game stories, movies, what-have-you.
For example, Tolkein fleshed out a huge and detailed universe in his works. There's plenty there to draw from for everything from more novels, to games, and movies. But at what point are writers crossing from canon to non-canon? Was the universe ever "passed on" to someone who is in charge of it now? Is that even possible? Or is every derivative of his works just that: a derivative?
In the reverse, you could take the Battletech franchise. It was designed and written as a game, but then became popular enough to spawn a sizable amount of novels and video games. But who is considered to be the IP-owner that can say "Yes this is part of the universe" and "No that's not possible"? Or is there even such a person/group?