..... The FNAF franchise has been popular because of the games and fandom for several years, then several years later the book and movie managed to be sold, but I wouldn't give all the credit to the book by of the Indie game.
I believe you could rephrase your question if you're going to use non-Main Source Indie books as your focus but Indie content in general:
"Is Indie media doing good these days?"
Of course it is! And it has been for a while, but obviously whenever these independent or indie content gets serialized, goes under contracts, due to popularity and investment is that... it kinda of makes people forget they started as Indie Media.
Like the Mutant Ninja Turtles, it started as a self published comic (Fanzine) thus Indie, same for several people that make a living with their own content, be it books whose content is written, drawn and similar.
I don't know if you're pretty young, but I think you should... expand a bit more on the genre if your only cue to know if Indie books are doing good is through the announcement of the FNAF movie... And this is coming totally from someone that lives under a rock and barely consumes any media due to work and is a self-proclaimed ignorant in webcomics or Independent content in general.