Characters who self-identify as the biological brain consider it death, and being replaced by a machine.

Characters who self-identify as the jewel being bootstrapped / trained by the biological brain consider it no big deal, like removing training wheels from a bicycle.

That distinction stuck with me hard, for years. The same reality, different levels of suffering.

Seems to me like the only way to deal with something like dementia is to have a worldview where you aren't surprised and confused and afraid to wake up and not know who you are, where you are, or who people around you are. To have plans now for how you'd cope with it.

Because if you don't have that worldview now, in advance, you won't be coherent enough to change to it when you need it.

Or if you're going through a clone/destroy teleporter, or being mind-uploaded into FaceBook 2070, or get alcohol induced long term memory formation problems, or are going to offload parts of your thinking to brain implants or desktops ... lose your identity now, so your pattern won't include suffering later as it carries on.