Generalizing improperly from my own experience and that of people I know, it seems to me that it gets easier to accept the idea of death for many people as they age. Hopefully we'll crack the aging thing ASAP, but I wonder how many will die of old age even after aging is more-or-less optional.

While I'm too young to say, I think at the time you are old, your brain would have changed (or degraded) sufficiently enough to handle it with relative ease. That's the only way it makes sense to me when I read about ailing people talking about seeing the exit, the final candle, or whatever.

That aside, I also consider "what happens after you die" to be the ultimate question. Because nobody alive, dumb or smart, knows the answer, and nobody has come back to tell us. It just depends on when you think you are ready to find the answer. Perhaps after you solve the unified field theory everything will converge.

Even if true, not everyone would die after their brain has degraded in this way.

Sleep disorders are quite common in the elderly and I would guess that this is mostly due to a fear of death while asleep.