The diagnosis of a legendary women's basketball coach at my school, Pat Summit, with early onset dementia, Alzheimer's type, got me thinking about Cryonics and Alzheimer's. For the purposes of this thought experiment, we will ignore the legal implications of the fact that you can't be frozen until you are legally dead. Let us further assume (which given my knowledge of Alzheimer's, is pretty reasonable) that the damage done by Alzheimer's is complete, and that future technology will be unable to reconstruct the destroyed components.
If you were diagnosed with Alzheimer's, or really any neurodegenerative disorder, at what point in the degradation would you want to be frozen? This would fairly easily prevent further degradation, but might further damage you/all of the other risks associated with cryonics that everyone knows. Obviously, you wouldn't have the agency of mind (or perhaps you still would, depending on when you made the decision) to do it yourself, but suppose you were caring for a loved one, or writing a living will. Assume you operate healthily at the onset of your diagnosis.
Things to consider:
How would your loved ones react to your being frozen versus coping with you having Alzheimer's? Should this matter in your decision? If it does, what implications does that have for a duty to die?
How much degradation of the mind is acceptable (and the added damage potentially done by cryonics) before one should freeze onesself?
Would you avoid the risk of being frozen all together because you believe we will or may have a cure for Alzheimer's soon, and waiting for it would do less damage than cryonics?
My priority would be to minimize damage, so as early as possible while still allowing for the least traumatic transition for family and friends. I expect it would be the same as dying suddenly: lots of paperwork to do, translating into stress added on top of grief.
Which, of course, is a strong argument for advance preparation.
The same applies for sudden death or severe illness. At 40 it's a bit early to be thinking a lot about this, but definitely coming up as a to-do item; I've just been reminded by Steel's The Procrastination Equation that this kind of planning is something many, many people procrastinate about (sometimes until death).
Not in the current state of knowledge about the disease. Onset-to-death times are in the range of 5 to 8 years apparently, which is just barely enough time for a new cure to make it to widely available trials, not enough for it to be more than a very long shot. But in the meantime your personality would be slowly disintegrating; by the end of that period there wouldn't be much of a "you" to benefit from the cure.