Sad as it may be. GRRM did supposedly give Benioff and Weiss some of the major points of the ending. I'm assuming things like Daenerys burning King's Landing and Bran being king are going to happen in the book, or at least they were at the time he laid it all out for them. It's always possible Martin may change that given how things went down but even if those plot points remain the same, it's a given that it'll be done in a better way than the show because there's still over 2,000 pages to go so it won't be rushed.