I think to understand this question, we first need to look at how the line got started in the first place. As much as you may like to think so, it wasn't like LEGO woke up one day and said, "You know what would be awesome? A Star Wars line!" No, the decision was based on the fact that Lucas was releasing the new films, and that Star Wars was again being brought to the forefront of popular media. As popular as it was, there is no way the OT could have sustained for more than a few years, especially without new media to attract younger buyers (the primary consumer of LEGO products).
However, with three new films being released (particularly ones featuring new vehicles and characters), LEGO would have plenty of inspiration for new sets while also delivering classic sets as well. Why do you think the original end date was 2007? By this time, all of the new films would be released and LEGO would have had plenty of time to develop sets from the movies. However, by 2007, it was probably assumed that people (young people in particular), would be "over" Star Wars and would have moved on to the next thing. Obviously, some would remain true, but there would be diminishing returns each successive year.
However, Lucas then announced the Clone Wars movie and TV series, along with a new live-action TV show. Just like that, Star Wars was back in the limelight and LEGO had reason to continue the line. It was probably tentatively assumed that these new media would create enough inspiration and attention for sets to last through 2011.
So will LEGO cancel the line after 2011? I think that depends on the fate of the new TV shows. If they continue to be popular and get picked up for more seasons, I think it would be very likely that LEGO would renew the license. However, if the new shows fizzle and fade quickly, and Lucas doesn't try any other new movies/shows (with Lucas, you never know), I would think that LEGO would probably wrap up the line and move on. It's foolish to think that young people (again, the primary consumer) will continue to be drawn in to Star Wars without new media to draw their attention. While it's a nice sentement to think that LEGO would continue the line for AFOLs, we all know that that's just not going to happen. And as much as we'd love for them to delve more into the EU (I, personally, would lose my freaking mind if LEGO ever released sets from the Thrawn trilogy), they just don't have the cache to reel in new buyers. No, my friends, love it or hate it, the fate of the Star Wars LEGO line is currently tied to the continued success of the Clone Wars series
Just my thoughts...
The beauty of a LEGO MOC is not the elements that go into it, but the way those elements are put together.