SpongeBob SquarePants as we know is a cash cow, very much the longest running Nicktoons Show of all time to point of being the only one that premiered in the 20th Century that's still around to this day. Being a cash cow, people have been saying things about the network refusing to cancel the show, but at the end of the day there are shows we didn't think would ever get cancelled that did get cancelled eventually such as Rugrats and Fairly Odd Parents. These have not always been the network's decisions I should add, for instance with Rugrats it coming to an end was as a result of the 3rd feature length Rugrats film Rugrats Go Wild being a flop, so perhaps that's what it'll take with SpongeBob as well. But one thing that should be kept in mind for if the upcoming 4th film does flop, those working on the show should be given time to work on an ideal closing point for it where we are able to see what is able to be an indicator of it as the finale.