His biography _A Life With Footnotes_ by his assistant describe how the last books were made. Pratchett would still have moments of clarity when he would dictate whole scenes in an almost finished state, but he wasn't able to tie them together into a whole anymore. That was mostly done by an editor. And large parts of the book are only sketches of a plot that he would have kept editing and expanding over and over normally, but there wasn't time.

I still thought it worked as a fitting end for many characters.