Yeah.... We're going through much the same currently with my grandmother. Sad, and terrifying, in nearly equal parts.
I do not look forward to those days with my parents. After dealing with her own mother for the past few years, my mom now has a common refrain of "If I ever get like this, just take me out back and shoot me."
In an episode of The West Wing I remember about the subject, they referred to it as The Long Goodbye. I think that's appropriate.
I can say, though, there is some amazingly promising Alzheimer's research happening right now. Unfortunately, they're certainly still at the basic research stage, so clinical trials (if it gets that far) won't be for way too long to help anyone suffering right now. However... If you are a mouse (and, yes, mice get Alzheimer's too), there's a good chance you can be cured right now. That is a Very Good Sign for the future.