No, SpongeBob is no where near to being cancled. The only ways that SpongeBob could be cancled is if there's a decrease in television audience or the producers has ran out of ideas for newer episodes. Did you know sometime in 2011, SpongeBob will be the longest running Nickelodeon cartoon/show ever? It will top the Rugrats. At the rate SpongeBob's running, it will become the second-longest cartoon to be aired on telivision right behind the Simpsons.
The reason SpongeBob's been on tv for nearly 12 years is because both children and "adults" love watching the show. With the mixture of child humor and adult humor, the viewer audience is increased which keeps the show up and running.