He needs to hand his "notes" to one of his competent author buddies to be completed in the event of his death.
I would nominate Gardner Dozois
but that guys in even worse shape than Martin!!!!!
Hmmm. Maybe China Miéville
is available. I'd love to see that dude's version of post-doom Valyria. Miéville generally hates traditional fantasy, but I'd bet even he would concede that Song Of Ice and Fire is NOT traditional fantasy.
Oh, THIS happened:
You know, I asked George Martin about who Jon Snow's real parents were, and he told me. I can't say who, but I can tell you that it involves a bit of a Luke Skywalker situation. It will all come to fruition eventually. The whole thing with all the fight over proper succession is partly inspired by the War of the Roses in the late 1400s, and back then, to ensure pedigree, the monarchies were kind of inbred. It's definitely fucked up, but it definitely happened back then, so that's why there's incest with the Targaryen line. It's toned down, though.
Sounds to me like Ned Stark isn't Jon Snow's father.