I'm not sure if you could really consider the whole DCAU a whole series since I always thought it was more like different series that are set in the same universe. Besides that, I wouldn't say that 2k3 fails if, key word if, it doesn't go past the episode count of the original series. While it varies for different people, I always preferred quality over quanity when it comes to watching series.
Like Toon Out mentioned, TMNT is still a profitable property. The 80s series was popular and did well and while the 2k3 series hasn't been as popular, it still has done well enough from what I can tell. I wouldn't mind a new continuity, if they are ending the 2k3 series, as long as it is interesting.
While I'm not too familiar with how they're doing finanically right now, I haven't heard anything about 4Kids possibly going bankrupt anytime soon. So I really don't see how you could come to that conclusion.
You do have a point about how a show can be more rememberable if it has an impact on society. However, as Toon Out already mentioned, it really helps that those old shows were in syndication for years and those characters have become icons of the time. While there's no gaurantees on how a show will be remembered after it ends, with the different means of viewing shows nowadays, such as DVDs, TV, the Internet, and having over 150 episodes so far, there's a good shot that TMNT won't just fad away.
No offense, but I think that you're kind of generalizing people. I think that would apply more to the people who grew up with the 80's cartoon series. The kids who weren't born during the series' run would probably recognize the turtles from the new series or from the movies. In all honesty, before I watched the 2k3 series, I always thought of the live-action movies whenever I thouight of the Ninja Turtles.
I'm not so sure about that. I could see TMNT getting some more ratings, especially when the ratings for Pokemon and Yu-Gi-Oh! were in their prime, but I'm not sure if that would make it more popular. Other than Pokemon and Yu-Gi-Oh!, the only other shows from Kids' WB that I think gained a strong amount of popularity were The New Adventures of Batman and Superman, possibly Batman Beyond and Xiolian Showdown. Maybe you could argue the same for Jackie Chan Adventures, at least the early seasons, but just because something airs on Kids' WB doesn't really guaretee that it would be more popular.
As for the topic at hand, I'm still kind of skeptical about TMNT ending this year since I have yet to see a reliable and official source for that information. I personally don't consider fourms or a blog official unless the person is directly connected to the show, which has yet to be seen so far. If this does turn out to be true, I don't think I would mind that much either. I have enjoyed most of the episodes for Back To The Sewers, but I do agree that it doesn't capture the same feeling as the first five seasons of the series. In all honesty, as long as the series has a satisifying conclusion to the storyline, then I'll be happy with that.