La question est un peu étonnante mais elle fait l'objet d'un article en anglais ici


Je vous mets le début

"Which SF writer has made us wait the longest for a sequel?

C.J. Cherryh's Regenesis, the sequel to her Hugo-Award-winning Cyteen, was released this month to the delight of her patient fans. We've been waiting for this book since 1988—a span of time during which potential readers could have been born and nearly earned their college degrees!

But Cherryh is not alone among SF authors in keeping her audience waiting on tenterhooks many years for the further adventures of a favorite character—or even for the resolution of a cliffhanger!

To learn who had the longest gap between a book and its follow-up, check out this list of the Top 10 Longest-Delayed Sequels.

1) Jack Vance's The Palace of Love (1967) and The Face (1979)

Kirth Gersen's quest to kill the five Demon Princes who destroyed his world took a break of 12 years. But he caught up with villain Lens Larque at last, before moving on to Howard Alan Treesong in the final volume.

2) Philip Jose Farmer's The Lavalite World (1977) and More Than Fire (1993)

Sixteen years separated the penultimate and final adventures of Kickaha in the World of Tiers. But the concluding volume in the series did pay off with answers to the various mysteries of this strange cosmos.

3) Jack Vance's The Eyes of the Overworld (1966) and Cugel's Saga (1983)

The Dying Earth's chief rogue, Cugel, disappeared for 17 years. That is, if one does not count Michael Shea's intervening authorized excursion, A Quest for Simbilis (1974).

4) Tanith Lee's The Silver Metal Lover (1981) and Metallic Love (2005)

Readers had to wait 24 years to learn more about the love affair between Jane and her android partner Silver. That's undying love!

5) Isaac Asimov's Second Foundation (1953) and Foundation's Edge (1982)

It took 29 years for Asimov to return to the fan favorite Foundation saga. Winning SFWA's Grandmaster Award in 1986 coincided with a fifth book in the series."