That's too bad. Kinda selfish in a way.
I make it black and white but it's not obvious to me you always want to publish things just because some people will devour them.
Since you'll be dead and utterly unaffected either way, I'd go with pleasing the fans. Also, it's really a freebie for your legacy if it's understood that it was written under the influence of dementia and published posthumously.
On the other hand, if I thought it would be depressing or unpleasant to fans more than please them, I would want it destroyed.
But that's what I'd do. Terry Pratchett had every right to make his own decision on this. Even with dementia, that's 100% his call. (Of course, his assistant should make sure he was fairly consistent on this point, when most lucid.)