The announcement that Amazon Prime would be producing Good Omens season 2 was met with mixed reactions from fans of Sir Terry Pratchett, who were fearful the project was more concerned with cashing in on the popularity of the television adaptation of the classic novel than honoring Pratchett's legacy. While these concerns are understandable, given the varying quality of other adaptations of Sir Terry's work, they are also unfounded, as Pratchett had plotted a sequel to Good Omens with co-author Neil Gaiman. Unfortunately, they never got around to formally writing it.
Gaiman wrote about the new series and his friend in a post on his blog, where he discussed how he and Sir Terry had planned a sequel to Good Omens before the original book had been released. Reportedly the two fully plotted the second novel over the course of a single insomnia-fueled evening while attending the 1989 World Fantasy Convention. Titled 668: The Neighbor of the Beast, Gaiman and Pratchett fully intended to get back together and write the Good Omens sequel once they had time. Unfortunately, both authors tragically found individual fame for their solo writing projects shortly thereafter and were soon too busy creating new works set in the Discworld or The Sandman Universe to get back together and actually write 668: The Neighbor of the Beast.
The existence of 668: The Neighbor of the Beast had been confirmed in earlier interviews by both Neil Gaiman and Sir Terry Pratchett. As such, there's no reason to believe that Gaiman is now lying about having a story worked out, just as new fans are clamoring for a follow-up to the Good Omens series despite its quite definitive ending. Given that, and Gaiman's own track record for being choosy when it comes to whom he allows to adapt his work into television or film, there is every reason to believe that Good Omens season 2 will honor Pratchett's legacy and be written in a tone consistent with his oeuvre.
The fan fears about a Good Omens sequel being nothing more than a cynical cash-grab are easy to understand, given the disastrous premiere of The Watch earlier this year. While being said to be "inspired by" the works of Sir Terry Pratchett, the resulting Watch series bore little resemblance to the Discworld novels, seemingly applying random character names from Pratchett's books to its original characters. The series was roundly condemned by Sir Terry's family, friends, and fans, with Gaiman himself comparing it to a Batman adaptation where Batman was "... a news reporter in a yellow trenchcoat with a pet bat." Thankfully, all signs point to the Good Omens follow-up being much more respectful.
After all, Gaiman will return as co-showrunner for the new season alongside Douglas Mackinnon and together they will bring answers to fans about what the angel Aziraphale and demon Crowley have been up to. Given things are still in the early stages of development - it won't film until later this year in Scotland - it's unlikely Good Omens season 2 will air until late 2022 at the earliest.