I haven't finished it yet but I have read the book. Didn't they basically cover all the content from the book in season 1? I can't imagine additional seasons would be nearly as good with show runners just making things up off the cuff.
This is my worry as well. I didn’t read the book but as far as I know season 1 already covered it. If they base successive seasons on actual historical events that the book was based on, maybe it can work?