Accidents can happen people can get run over by a bus, or be in a terrorist bombing incident, or die in a plane crash, or have a brain aneurism.

Whereas Robert Jordan had time to find a replacement author and tell him all the important remaining plot points to get TWoT finished, if there is some sudden thing that happens to GRRM from finishing the books, the end and the main plot points leading to the end are known by David Benioff & Dan Weiss (GoT Producers). So what would you want D&D to do with that knowledge if the worst case scenario happens?

Should they finish the story of ASOIAF only through the TV show? Or should they write (or help someone to write) the final book(s) and then perhaps complete the TV show? Or complete the TV show then finish the books? Assuming of course that the TV show remains sufficiently popular to finish the entire story on screen.

Just finish it through the TV show. (Like they will anyways if george doesn't pick up the pace)

Fuck. I hope not, but likely as previously pointed out through a tv show, they have the setting, the characters etc. unless they also have his final notes, they will have to improvise how it all ties together I guess, but it will be hard to find an ending that will please all the fans, no matter whether George writes it or the show

first world problems in here I see.

Has it been said that they will? They seem extremely book accurate so far.

They will run out of books after the sixth season at present; I doubt actors of the caliber included will want to do seven consecutive years of work on this.

Well, that question is kind of for everything.... What if J K Rowling died before the Harry Potter books finished, Oda with One Piece, etc.

Actors can work on multiple projects in one year. I assume this is why you are saying this?  Leonardo has done 3 movies in the last 12 months for example.

I doubt it would be a problem. He'd have the main story worked out in his head already I imagine. It's probably written or typed down somewhere too. Little things would be subject to change though. Most writers do that don't they? Or something similar. JK Rowling comes to mind.

Filming on GoT was July-November for the last season. I don't think more than one other project would be possible, at least some of the key actors will find this limiting eventually. Eight years? I mean the child actors will have issues portraying their age as well.

Targaryan scenes only took 3 weeks to shoot if i remember right.  The show in a whole is huge however for each actor it is much smaller since there is soooo many actors.  Most of the work will be flying, directing, putting scenes together, editing etc.