I don't see it as offensive. As otheres have mentioned, it has happened before. I know that Stephen King was really concerned that he would die before finishing The Dark Tower, and that he maybe rushed it.
I hope Martin lives as long as possible, but I do secretely hope he continues to write so slowly that the HBO series actually gets ahead of the books. I don't like his prose, so I have no interest at all in reading the books, but I do enjoy the shows. I generally feel that way about fantasy or Sci-Fi*. I'd just rather watch the movie/TV show or play through the world in a game. So, the small group of people who insist that I'm "doing it wrong" by only watching the show annoys me. I just like the idea of how much rage it'd generate for that group if those lazy-bones dumb-dumbs only watching the show got to find out what happens first.
* Sci-Fi as in "fantasy set the future", like Star Wars. I might read actual Science Fiction.