Originally there was going to be a sequel right after Casablanca came out in 1942 called Brazzaville, named after the location of the Free French garrison mentioned in the film. In that film, it would be revealed that Rick and Captain Renault were Allied agents all along. Which instantly makes them boring stock characters and soon the treatment by Frederic Stephani was scrapped.
Casablanca would then show up on the small screen – first as part of a rotating segment on Warner Bros. Presents (along with another segment based on Kings Row!) in 1955, and later in 1982 for a Casablanca tv series that lasted a whole three episodes.
At that time Howard Koch (one of the three screenwriters who shared the Oscar) was writing his own treatment for a sequel, called Return to Casablanca, which included parts for still-living cast members (the scripts were rewritten when they died) centering around the son of Rick Blaine and Ilsa Lund – who was conceived the night Ilsa cam to beg for the transit passes – and then raised in America by Ilsa and Laszlo. Rick Jr. then returns to Casablanca in the 1960s to try and find his father, who disappeared during the war. There he follows the trail of ruins to find the fate of his father, helped by an Arab freedom fighter named Jane.
There was also a book sequel called As Time Goes By by Michael Walsh that saw Rick and Renault being recruited by Laszlo and Ilsa to assassinate Nazi leader Reinhard Hydrich in Prague (an actual event.)
Cass Warner, granddaughter of Harry Warner and grand-niece of Jack L. Warner (the real Warner Bros.) found Howard Koch’s treatment and is attempting to get Warners to give her the go-ahead to make it. They passed a year and a half ago, but said they’d be interested if she got a bankable director behind the project. Which means this could happen at any time! Be afraid, be very afraid!
(Also LOL at the NY Post article url being “Saloonkeeper Thanksgiving Assassination” for some reason!)