There's a lot of assumption here that the only reason for anyone to have watched the show was for Sean and that without his character the show won't be worth watching. Should Martin be a bit concerned? Probably, but that is simply because of the nature of telly shows that live or die according to the whims of network executives that are ridiculously reactive to ratings. The book series didn't end after just the first book. Did Lord of the Rings film 2 and 3 bomb after Boromir was killed off? LOTR went on to achieve far more after that and there weren't any actors that were considered top tier at the time. It had a great ensemble cast of character actors. I tuned in to the first episode of Tudors because Sean Pertwee was in it and then he got killed off in the first 5 minutes. But, it took just that one episode to hook me on the entire series. None of the big cable series featured any top tier actors. The Borgias features just one single actor who could be considered top tier and Jeremy Irons is really just a good character actor. He makes me cringe every time they show him in sex scenes. *ewwww... In fact, none of the biggest shows on network telly feature big actors either. They put together ensemble casts that often lose major charactors along the way. Look at all the big shows in the past 10 years and you will spot the trend right away: Lost, Gray's Anatomy, Desperate Housewives, etc. There certainly are a lot of good actors turning to telly, ie: Glenn Close in Damages, Timothy Hutton in Leverage, but they are actors that have been and would likely remain unemployed in front of the camera in the first place due to age. Would their series be less successful if they were't on those shows? Most likely, simply because the shows have great ensemble casts that do the big job of telling great stories. It rarely takes big name actors to make a successful telly show these days. We may have watched GOT simply because Sean was in it, but that's not what made it a great show. The books continued after Ned and Robert were killed off simply because they are great stories and trust me, there are far more fans of the books than there are fans of Sean.