Well, obliviously they knew that it would be the last episode of season 4, but they didn't have any idea what would happen after that. The complete selloff to Turner happened after the episode was completed, and even if they had known ahead of time that that was happening, nobody would have known what they were going to do with the IP.
LazyTown operates a lot like a cartoon, and there are 2 ways that cartoons usually end their run. They either don't have any kind of formal ending, or they have a movie. I would not be surprised to see LazyTown continue some day in some fashion, maybe just as a final movie type of thing, wrapping things up like you want, even if it takes 5 or 10 or more years to get that. I also would not be surprised if it never did get revived.