Great Creative and Fun Show

The writers/producers don't think it will ever return, as the season 3 finale is pretty definitive in that regard (or is it?).

It's not canceled, because Adult Swim keeps a lot of shows on hiatus, waiting for years for the writers to pitch them new ideas, rather than giving them a tight deadline. So, in the eventuality the main writers come up with an idea they're enthusiastic about, and Adult Swim agrees, the show is still officially on hiatus.