To be fair, it's not imminent Death that's the problem, really. Alzheimer's is not a cool way to go.
No way to go is a cool way to go....
Given that we all have to go someday, one can at least rank some as less awful than others. A slow slumber after a small injection versus having your mind sizzle away like butter on a skillet?
I watched my grandfather die with Alzheimer's. I cannot think of a more appalling situation. (The "good" days were the worst; he knew what was happening, then, saw himself soiling his bed and helpless. He said something once that has always struck a chord of utter desolation inside me. He looked up at my aunt and said, "I never thought it would end like this." Next minute he was gone again, sucked back beneath the whirlpool.) I would personally prefer total-body paralysis to that paralysis of the mind, that death of personality. To be trapped in a disintegrating castle, every day the rooms a little smaller, the corridors more jumbled... to me, that is one of the most horrible things I can imagine. And I get to know that I've got a far higher-than-normal chance of ending up with the disease myself, if I live long enough.
I'd rather go out as myself, not as a drooling husk with my face. I am normally virulently anti-suicide, but in this sort of situation it's more like conceding the game once the checkmate is inevitable.