I'm sure I'm not the only one who greatly admired him. The theme of his stories was progress; they were set in a fantasy world, it's true, but one that was frequently a direct analogy to our own past, and where the golden age was always right now. The recent books made this ever more obvious.
We have lost a great man today, but it's the way he died that makes me uncomfortable. Terry Pratchett had early-onset Alzheimer's, and while I doubt it would have mattered, he couldn't have chosen cryonics even if he wanted to. He campaigned for voluntary euthanasia in cases like his. I will refrain from speculating on whether his unexpected death was wholly natural; whether it was or wasn't, I can't see this having a better outcome. In short...
There is, for each of us, a one-ninth chance of developing Alzheimer's if we live long enough. Many of us may have relatives that are already showing signs, and in the current regime these relatives cannot be cryonically stored even if they wish to try; by the time they die, there will be little purpose in doing so. For cryonics to help for neurodegenerative disorders, it needs to be applied before they become fatal.
Is there anything we can do to change that? Are there countries in which that generalisation is false?
Decidedly mixed. In the very late stages of Alzheimer's large sections of brain tissue are literally gone. See e.g. here. On the other hand, even with fairly late stage patients they do have better and worse days where they remember more or less, which suggests that some memories are still present. We also know that in some animal models treatment can apparently restore some amount of memory. See for example here (which may be behind a paywall). That last link is to some very new, very recent research suggesting a form of high powered ultrasound may actually help Alzheimer's in mouse models, and there's decent reason to believe that this will work in humans.