Originally Posted by SixOhNine
was hideously expensive and HBO didn't have full control of production, so the decision to kill it was somewhat out of their hands. Carnivale
had terrible ratings and uneven (at best) storylines. I don't think those are solid comparisons to the runaway train success of GoT.
That said, if GRRM keeps his current pace of one book per 6 years, HBO could easily kill it rather than keep carrying the expenses of contacts, locations, sets, etc. on the books forever.
I'm quite confident HBO would move to make the final season without the book being published.
I wrote more about this earlier, but it looks almost certain that the series will be able to make it through the next book, The Winds of Winter, with source material having been published. It's after this that things get hairy, but I'd wager that HBO just makes the next season anyways--they already know what is happening. There may be some small differences, but there already are, and the downsides to this approach are far less than those of waiting.