Alice: If you are looking to continue the story, I strongly recommend listening to the Know Direction Paizocon 2016 Pathfinder Compatible Publishers Workshop podcast. Looks like it's PaizoCon2016 number 040.
Here's what (I recall) you can do: Anything you write as a follow up to what is currently published will need all new NPC's. For instance, if you want Knivy Ivy to continue as an NPC, she cannot without Gary's Permission. However, you can introduce a new, eerily similar NPC for the players to meet. Also, you won't be able to reference any proper nouns from Throne of Night. You won't be able to use any art from Throne of Night.
I'm not trying to discourage you, I'd love to see your work. But I don't want to see you get in trouble either.