There are 3 unfinished episodes after Swat Kats episode "Unlikely Alloys". They are The Curse of Kataluna, Turmoil 2: The Revenge, and Doctors of Doom. The Curse of Kataluna is also known as Succubus. All of these 3 unfinished episodes are written by Glenn Leopold. You can get some informations from Mark Lungo's Article of Swat Kats, which was released on Animato Magazine in 1995. Movie "Scooby doo on Zombie Island" is based on Swat Kats unfinished episode "The Curse of Kataluna".
The reasons for the cancellation of SWAT Kats are unknown. SWAT Kats was doing very well in the ratings. Due to high ratings between August 30, 1993 and April 17, 1994, SWAT Kats became #1 new syndicated cartoon of 1994 . The rating results were approved by Nielsen Television Index (NTI) and Nielsen Syndication Service. Hanna Barbera Productions promised fans that they are going to release more episodes in 1995. And they even released a full page ad in October/November (1994)issue of Animation Magazine. But that never happened to this successful show. Turner Program Services ordered to cancel the show, while they were finishing Second Season. Christian Tremblay and Yvon Tremblay (Creators of SWAT Kats) became surprised when they heard about the cancellation of the show, because the show was doing really well in the ratings. Many fans sent letters to Hanna Barbera Productions about this subject. But Hanna Barbera Productions didn't replied to their letters probably because of the financial disaster they had with Jonny Quest Real Adventures.