The Simpsons is currently the longest American animated show with 520 episodes. The second longest is yours truly, Arthur. As for whether Arthur can outlast longer shows it depends on what keeps it going. Like Arthur should try new things. Things that have never been done before that can attract children as well as families in general. The Simpsons manage to keep going, but recently has had some close calls. It has been renewed for two seasons. How long that will last is a mystery at this time and depends on the production team of that show. They have to like do something that can really impress fans and at the same time can keep the show around longer. That's what Arthur needs to do.