I can't believe they would cancel Spongebob... the creator especially. Think of all the money this guy is making not just with the cartoon, but t he mass marketing of Spongebob products... I don't know why he'd just suddenly stop.
Plus Spongebob was named one of the best cartoons of all time (I'm really embarrassed to know this
)
If you are talking about the petition on that gopetition.com , I seriously doubt it is a credible source -- they even have petitions for 'pro-anorexia'
So until you hear the news from Nick. ( the network!) I think Spongebob will be just fine.