That's something I have thought about as well, but realistically I fail to see how this is possible to escape it completely, since most of the time, when you have dementia, you simply don't realize you have it (or, you deny it).
The interesting part is he could not remember the word for it, but the part of his brain that knew what dementia was, still functioned.
So he would say, "I have that thing that starts with the letter d, where I can't remember things".
I also remember after he passed, going through things in his home, and finding papers and things he had collected, which were his reminders to himself that he had seen in himself that he couldn't remember.
I think for me, one of the most emotional moments I had was finding this poem printed and sitting on his desk: https://www.ellenbailey.com/poems/ellen_112.htm
I still miss him and was in awe of the fact that he was going through the stages of dementia but still remembered me, and was aware of it. I think being aware of it almost made it worse, in my opinion.
In Oregon, there is/was an effort/lawsuit by one person in early stages of Alzheimer's to allow for physician assisted suicide after diagnosis. Currently one of the requirements is such that it precludes being used by dementia patients. Just Googled it - she had to move to another country to get that assisted suicide.
There are other anecdotes of people being aware they're falling into dementia. I know a famous writer whose mother knew it and asked him to kill her before it got worse (he refused).
So I wonder what proportion do and what don't.