With Game of Thrones functioning in part as a response to and a subversion of Tolkien's Lord of the Rings I must say that never finishing the story fits perfectly. Instead of your son protecting your most important literary contribution and stewarding it through the decades you instead don't never have kids and order your wife to destroy your notes when you die. Write it in to your will that no one else may pick up the pen to try and rectify your shortcomings. A satisfying conclusion shall never be provided because life so rarely does.
Bravo Martin. Bravo. I hope that you inspire new generations of authors to write their own stories influenced by the path you forged and subversively fucking finishing what they fucking start.