Phineas and Ferb has been running much longer than the majority of other Disney Channel Original Series. I haven't seen the finale special yet, but I've heard that it does give the series a sense of finality. And in Disney, nothing is forever. Things are constantly changing, improving, and renewing. Though people may be sad, we can be sure that Disney will do it's best to create a new show that will satisfy fans as much as Phineas and Ferb ever did.