In an interview reprinted in The Salmon of Doubt, Adams expressed dissatisfaction with the "rather bleak" tone of this book, and said that he "would love to end Hitchhiker on a slightly more upbeat note" by writing a sixth installment in the series. He blames personal problems, saying "for all sorts of personal reasons I don't want to go into, I just had a thoroughly miserable year, and I was trying to write a book against that background. And, guess what, it was a rather bleak book!" Nonetheless, the story does a good job of tying together most of the plot elements introduced in the previous novels, in a typically quirky fashion.
Being the fifth book in a trilogy, and Adams wanting to write a sixth one, it wasn't entirely granite that this was the concluding book in the series, until his death (due to a heart attack) on May 11, 2001 made it so.
Although the complete destruction of every version of the Earth in every possible timeline, along with the death of nearly all the regular characters would seem to make a continuation extremely unlikely, Adams had remarked that the afterlife-enhanced state of the regulars merely meant he would not have to waste time at the beginning of the next book gathering them together or explaining what they'd been up to in the intervening period.