A Dance With Dragons is the last available book currently.
At this point in the TV show, the story lines have moved far away from story lines in the books.
I have given up on the books after reading all 5 of them twice.
I don’t think martin will ever finish them. I think he lost his connection to the characters and story.
Martin won’t finish because the internet caught up to him. His whole drive was to unveil that John Snow was the offspring of the Mad King and Ned Stark’s sister. Before the internet, maybe a few people would have figured it out. Because his books are so popular, whole fan sites formed, communicated, guessed the ending, and took away his drive. He has threatened to kill off everyone in a twenty page book as a giant “screw you” to people who spoiled his ending. I can see his point and he doesn’t look to healthy.
I wonder if the show is going to try to conclude the plots of the books in case Martin never does, so that there IS an ending even if unofficial.
I don’t think there is any reason to believe Martin lost connection with his characters.