If it pans out this way, it should surprise absolutely no one. I don't see how the show doesn't end up "spoiling" the ending though. HBO ain't stretching this out (at least) seven more years.

http://www.avclub.com/article/you-might-have-wait-george-rr-martin-write-three-m-205364?utm_source=Facebook&utm_medium=SocialMarketing&utm_campaign=Status:2:Default

You might have to wait for George R.R. Martin to write three more books, actually

By Sean O'Neal Jun 3, 2014 4:38 PM
While fans, TV producers, and even George R.R. Martin himself have only become more vocally anxious in recent months about the wait for Martin’s sixth and seventh novels in his Song Of Ice And Fire series, now his editor has given you something else to worry about: an eighth novel. Anne Groell recently submitted to some fan questions on Suvudu Universe, where she was asked whether she really thinks Martin can wrap up the whole saga in seven books. Her answer is unlikely to comfort those who have thought that their current wait was somewhat close to over—or had already been somewhat defined.

"I begin to wonder — though 7 is what we currently have under contract. I remember when he called me, years and years back, to confess that his little trilogy was...well...no longer a trilogy. He predicted four books. I said Seven Books for Seven Kingdoms. Then he said five books. I said Seven Books for Seven Kingdoms. Then he went to six. I said...Well, you get it. Finally, we were on the same page. Seven Books for Seven Kingdoms. Good. Only, as I recently learned while editing THE WORLD OF ICE AND FIRE (another awesome thing you must buy when it comes out!), there are really technically eight kingdoms, all having to do with who has annexed what when Aegon the Conqueror landed in Westeros. So, maybe eight books for Seven Kingdoms would be okay. Also, he has promised me that, when he finally wraps this great beast us, I can publish the five page letter outlining the bare bones of the “trilogy.”"

While you’re still awaiting the publication of that possible eighth book—and that letter, which Martin already wrote, at least—Groell gave an update on book six, The Winds Of Winter, which she believes will be out “reasonably soon.” According to her, Martin gave her 168 pages a little more than a year ago to meet a contract requirement, and “I know more exists, because he keeps talking about chapter he hasn’t yet sent me.” In the meantime, Groell reminds readers that she’s been as patient as anyone, even raising “a two and a half year old walking, talking human being“ while waiting around for one. Who knows how many children she could raise between now and an eighth book?