Drakes According to him there's still 2 books left to write. Judging by the glacial speed he's writing with...well, if you want to see it finished first, come back in a decade.
Mark Gould There are currently 5 books released in this series. The last one was released in 2011, and the next one is likely to release in 2016. There is supposed to be only one after that, but Martin is famous for making the series longer than he initially thought it would be. It was originally envisioned to be a trilogy.
Jane It seems like he'll keep it up forever. He can always kill off characters and add new ones. Maybe I'm a cynic, but as long as royalties keep rolling in, I believe he'll keep on writing.