He always stated in interviews that the series was supposed to end in book 12, no matter how long he had to make book 12.

He spent the last few months of his life dictating notes on book 12 to his wife and son.

He, and they, said he had finished this. They have all the notes, the complete story, and how he wanted it written.

So when they come out with the book, which they are working on now, it shouldn't be too far off from what he would have written.