I work with Alzheimer's patients. A lady I sit with on weekends has gotten to where she's bedfast, at times doesn't even know who she is, needs to be spoon-fed, etc. etc. She got to that from being an extremely active member of our community. And I can't imagine that she anticipated this end to her life, or that she wouldn't have actively considered this knowing what her life has become.

If this is the decision that Sir Pratchett has made, then I can only support it, and hope that he gets to go with some dignity.