I have to say that I disagree.
An author's wishes should always be honored where his/ her work is concerned.
Regardless of what you thought of Pratchett and his writings, the final decision should be his.
If he wanted his writing carreer to die with him, who are we to disagree?
As I mentioned in the original post by @s0u1, where does it end?
Do we have modern painters "finishing" the sketches and doodles of the past masters?
A man (or woman) should have the final say as to the disposition of their legacy.
Just my thoughts.
Be well.