There are nearly 40 volumes in Terry Pratchet's Discworld series, so adapting it will likely be a matter of picking and choosing what stories to use and what to leave behind. Or it could be something that runs on television for 50 years like Doctor Who.
It doesn't really matter what stories are adapted so long as this hypothetical director retains the series' very specific form of fantasy and farce. It's also going to take someone with a strong eye for visuals. This is about a flat world which rests on the back of elephants who are riding on the back of a giant turtle, after all.