As requested by /u/clearance_unicorn and /u/viell, here is a summary of the "amicable divorce" discussion in Fire Cannot Kill A Dragon.

I'll just premise this by saying that even though I wasn't going to buy this book, because I didn't want to give any more money to anything associated with the show, I am glad I changed my mind. It's an entertaining and interesting read by someone with excellent contacts, and although generally favourable, it is most definitely not a hagiography.

Anyway, the chapter that the 'divorce' is discussed in is called "the Forks in the Road." I extracted some quotes from it below, but this summarises the chapter more fully.

The chapter opens with George talking to Hibberd in a restaurant about how he met DnD, and the things he won and lost by becoming famous. George then points across the dining room and says that 'right over there' was where he...:

"sat with Benioff, Weiss and Cogman in 2013 and revealed his long-held secret ending for A Song of Ice and Fire. By that time is was clear to Martin that the show would have major divergences from his novels."

GRRM then talks about the pilot reshoot, and how he realised he was losing his creation, giving the adoption analogy quoted in the post below.

DnD and Cogman explain a bit about why they made changes, and give as an example the decision to have Joffrey cut out a minstrel's tongue. Again, the quote is below I think - but in summary, they knew changing that up had ramifications for Lysa's murder reveal, but decided that they would figure out what to do instead when they got to it. One might suggest the ramifications of "figuring things out when they got to it" became pretty obvious in season 7 and 8, but moving on...

George talks about the show catching up and his struggle with writing, due to expectations from both fans and himself:

"On Tuesday I think it's the greatest thing I have ever done...On Wednesday I think it's all garbage and I should throw it in the fire and start again.

So anyway, DnD say they "dug deep" for information, and Cogman talks about "learning a lot of secrets" and then figuring out "what will work in the context of the show."

Then we have the quote about how every character has a different ending:

GEORGE R. R. MARTIN: (author, co-executive producer) It wasn't easy for me. I didn't want to give away my books. Every character has a different end. I told them who would be on the Iron Throne, and I told them some big twists like Hodor and "hold the door", and Stannis' decision to burn his daughter. We didn't get to everybody by any means. Especially the minor characters, who may have very different endings.

(indulgent editorial comment warning: although I found this a bit ambiguous at first, in context, and given the change of tense, it is pretty clear George is telling Hibberd he finds if difficult to talk about his characters' endings, and that every character has a different ending in the books to the show, and the minor characters may have very different endings. Others disagree though.).

Hibberd then moves on to discussing the show outpacing the books. George was confident he would finish the books before the end of Thrones because he assumed they would adapt both AFFC and ADWD. Hibberd discusses the geographical split format, and then George explains that he intended on using the same structure as the Lord of the Rings:

"It all begins in Winterfell with everybody except Dany. They split up and split further and further. Everything is getting wider, and it's always been my intend to curve back. It's the same structure as the show, but David and Dan made the turn much sooner, and didn't introduce some of my new characters."

So it looks like the gang will get back together aka the show.

The showrunners explain that they felt the show needed to "stay focused on its existing cast and maintain the momentum of its established storylines" and they didn't want new characters and locations. Hibberd lists all the different storylines that existed by season five - but I found it both grating and amusing that at least 3 of the 9 listed (Sansa and Ramsay, Brienne going North and Jaime in Dorne) were their own creations, and substitutes for George's.

Benioff then explains that they never intended a 10 year adaption, and couldn't be faithful to AFFC - too many of their characters would be absent and that wouldn't work. "It's always been about adapting the series as a whole and following the map George laid out for us and major milestones but not necessarily each stop." (editorial: I took this to mean it was never, even at the beginning the intention to adapt the whole story faithfully - and fair enough too, because everyone agreed that that would not be impossible).

George talks about how he thought ADWD and AFFC would be combined, and at least 2 seasons, but "they really started taking shortcuts and cutting things." He talks about LSH here, Quentyn, Tyrion's journey and hook up with Illyrio and Jon Connington and Aegon.

Then we get Benioff's quote about not getting bonus points for being strictly faithful.

By April 2015, it was clear to George he wasn't going to get the book out:

"...it really took a lot of wind of out my sails. Suddenly, they were ahead of me. I should have gotten the last two books out sooner."

Then we have the discussion about LSH and the reasons she wasn't included, which have been quoted and discussed elsewhere, and some discussion about the wolves. They are harder to animate than dragons, because people know what they actually look like. They settled on just Arya and Nymeria. As Cogman explains:

"[they are] lone wolves. They can't go back to the way things were. It was also a foreshadow for what Arya was going to encounter when she reunited with her family."

Then we get to the key moment. After season 4, George began to stop writing scripts. He told producers he needed to finish his novels. Benioff explains:

"It wasn't a contentious thing, it wasn't a screaming match. He just felt like he needed to prioritise the book, and that made sense to us.

The words "amicable divorce" are not used, but that was the vibe I got reading it.

Hibberd writes that "[t]he showrunners then had to figure out how best to use what they knew of George's master plan to plot their remaining hours." They then talk about the "silver lining", and Weiss' comments about how "there's no reason we can see why you can't be thrilled and surprised and dismayed by both these two different versions of the world".

Hibberd concludes the discussion by observing that:

"Ultimately Martin and the showrunners are passionate creatives grappling with a staggeringly complex tale in two very different mediums. Despite their occasional disagreement, each side is respectful of the other, even in private. Benioff and Weiss never fail to express the magnitude of their respect for Martin's writing, while Martin is grateful for the show and says the showrunners did a great job overall despite aspects that he wishes were different."

Then GRRM talks about that "one thing Dan and Dave did really right" (quoted in an earlier post) being choosing and amazing creative team to bring the story to life. Apparently they worked well with the team and and they were heavily involved in all aspects of the production, from costuming to being on set. Lots of praise.

But for Martin?

Hibberd writes:

"...for Martin, being creatively involved in with Game of Thrones - and commenting on it publicly - became increasingly difficult after season 5. How can an author talk about, for instance, the Battle of the Bastards, when he likely has his own very different, yet still unpublished, version of the same battle in mind?"

Weiss acknowledges that the differences became hard to track:

"It is almost like George was in a weird science fiction movie trying to keep two similar-but-different universes in mind at the same time."

George concludes by saying it has been "an incredible ride, almost all of it has been great", and that while the show is the end for some, it isn't for him. He has a lot of work left to do.

After this chapter, George's quotes or mentions in the book get fewer and fewer, decreasing from every couple of pages in the earlier chapters, to a quotes or a mention every thirty or so pages in the later third. This reflects his diminished role in the show and its direction. Similarly, DnD and Cogman start talking more about the show, what we wanted and we did and we liked. I'd say, although this is just my interpretation, they feel the show is their creation, and something they shaped on many levels, much as the books are George's.

edit: typos.