But still, and this is just my own belief, I think anyone who has given the matter some thought and introspection, is afraid of the end of their own existence. There may come a time indeed when death is better than remaining alive, but that doesn't imply one has stopped fearing death.
I'd want to draw a line between fear (as a very specific emotion) and aversion/dislike/anti-preference, as those are quite different things but both can be referred to as "being afraid of X". There are many unpleasant, unwanted things that I don't prefer at all and would actively work to avoid or prevent them, but I'm not afraid of them in the emotional sense. And there are a bunch of trivial things that I am afraid of (i.e. I experience that emotion when thinking about them) but that are actually good for me and I'm going to intentionally do them despite the fear.
There is a natural aversion to death, however, I'd argue that a great many people (though probably not a majority) don't experience any significant active emotion (including but not limited to fear) when contemplating their death, and that includes "anyone who has given the matter some thought and introspection", especially among people who have had lots of exposure to actual death. Experiencing fear and all the physiological effects of fear when being in clear immediate threat of death is a natural reflex, but that doesn't necessarily happen in rational contemplation about the end of ones existence. There is such a thing as acceptance.
I understand what you're referring to though, and assume that the very few that have actually fully realised this (and not just on an intellectual level) are not really bothered with death, and not due to lack of awareness of it.