And I don't think "becoming an advocate" is perhaps worded strongly enough. A few choice quotes from something he previously wrote on the subject (the link in philk's comment):
"I live in hope - hope that before the disease in my brain finally wipes it clean, I can jump before I am pushed"
"I am enjoying my life to the full, and hope to continue for quite some time. But I also intend, before the endgame looms, to die sitting in a chair in my own garden with a glass of brandy in my hand and Thomas Tallis on the iPod - the latter because Thomas's music could lift even an atheist a little bit closer to Heaven - and perhaps a second brandy if there is time.
Oh, and since this is England I had better add: 'If wet, in the library.'"
"I have met Alzheimer's sufferers who are hoping that another illness takes them away first. Little old ladies confide in me, saying: 'I've been saving up my pills for the end, dear.'"
As terrible as death is, interminable, futile suffering with no hope of respite until the bitter end isn't necessary and isn't what most people want.