Just heard this too a real shame but he got out before the Alzheimer's really kicked in. I thought he was older though and despite only reading one of his books, I remember him well from the Sky At Night when he would appear regularly on that.
Ahh fuck. I used to love his books growing up. Death and Commander Vimes were my favourite characters. Seems like not that long ago he was diagnosed with Alzheimer's, no idea it had been 8 years. I'm glad such a brilliant mind wasn't completely taken by the disease by the time of his death. Discworld lives on.