I consider myself lucky that I haven't been that close to it personally. I had a grandmother losing it at the end, to the point that the last time I saw her (my other grandma's funeral) she repeated the same story to me three times. But she knew who I was, at least.
My wife's best friend lost her mom to early onset Alzheimer's. That was obviously rough for all involved. My wife has such great stories about her, but by the time I met my wife she was already so far gone that that woman no longer existed. She was the one that taught my wife how to make meatloaf, "how much do I put in? Until it looks right!", and my wife paid it forward teaching my son Rachel's meatloaf "recipe". She eventually I think had a fall and ended up with a brain bleed, and she was just so far gone that surgery [even if it kept her alive] wouldn't really improve her life, so they had to put her on hospice and just let her go.
I'd say that in most cases it's probably better to have someone pass from a disease where you have some warning than to pass suddenly, but I think Alzheimer's is the exception. Because you can't really effectively say goodbye to someone who no longer inhabits the body that's breathing before you.
Medina, my thoughts are with you, brother. Good luck, and sorry you [or anyone] ever has to deal with this.