The panel was pretty cool, a lot of staff from the show talked about what they did and the huge process it takes to make a show like TMNT. A good majority of the staff was newer though (most started working on the show on season five or after), which accounts for the change in style and writing in the later seasons.
They also hinted at the DTV where "past characters meet present characters" but they couldn't say much more than that. Llyod Goldfine also expects to do another season, though so far he's unsure about the details.
It's obvious that there were no plans to make a new season for fall 2009. At the end of 2008, they were still working on new Back to the Sewer episodes, and now they're working on the DTV.
Besides, as was mentioned at the panel, most of the staff on TMNT also work on other 4Kids shows, so it's not like the TMNT staff will be fired or anything. There will always be the option of doing another season as long as 4Kids exists.