I'm not entirely out of new-to-me Pratchett to read; the fourth Long Earth book co-authored with Stephen Baxter is still in my to-read pile (and, according to the afterword in "The Shepherd's Crown" a fifth volume in this series was written before his death). But there'll never again be anything quite like Discworld.
We will, of course, be hoping very VERY hard that nobody gets the notion of hiring some other writer to attempt to continue the series. Because ... no, just NO!