I noted the announcement here on Book Chase on December 12, 2007 with some detail about why Pratchett had decided to go public about his illness.
Now, according to the Guardian, Pratchett is ready to consider his options before it is too late for him to have a say in how the end of his story is to ultimately play out:
Sir Terry Pratchett, the fantasy writer who was diagnosed with Alzheimer's in 2008, said yesterday he had started the formal process that could lead to his own assisted suicide at the Dignitas clinic in Switzerland.Sad as this is, it brings to mind the even sadder end of one of Pratchett's fellow British writers, Iris Murdoch, in whom the devastating disease ran its full course before her death. Unfair as I know it is, it somehow bothers me more when Alzheimer's claims one of the world's great thinkers than when it strikes a more "normal" person. I know just how unfair that feeling is because, as I type this, we are dealing with what the disease is doing to my mother-in-law, one of those more "normal" victims. What a horrible, horrible disease this is.
Pratchett, whose BBC2 film about the subject of assisted suicide is to be shown on BBC2 tomorrow, revealed he had been sent the consent forms requesting a suicide by the clinic and planned to sign them imminently.