I have no idea whether to a life fully keeps the fear of death away, what I know is that since I was a kid, I have been interested in death. Not in a morbid way, but I asked many times my little self what was the meaning of life, why we have to die and what happens after death. Humankind has always questioned itself about it and created many different theories or beliefs to console itself or to feel better about the fact that one day, we will reach the end of this journey.
Despite the different beliefs and the different concept of the afterlife, one thing it came immediately clear to me, one day willing or not this is going to happen.
How it's going to happen or when it's going to happen, it is not up to us, unless we decide to end our lives on our own will.
The only thing we know is what has happened in the past and what is going on right now, so with this knowledge we try to forecast and to make a sort of plan for our lives, but then... Yes, then it happens and final day arrives.
I believe the fear of death is not connected with an unfulfilling life, as someone said that for those who are living a life of suffering death is welcomed as a relief. However, for those who are living a happy life, leaving is going to be more difficult. Who would like to leave something pleasant?
From my point of view, the fear of death comes from not being willing to accept it or to even acknowledge it. Once I understood that there was nothing to do about it and that life, as it is designed for this planet, means just fulfilling a biological cycle, the same that is designed for all the living creatures either belonging to the animal kingdom or to the vegetal kingdom (birth, growth, reproduction, death), accepting it came easier.
Yet, death means just a re-arrangement of our molecules, and the creation of food for other forms of life, at least on the material stage. Then if we want to take into account what is going to happen to our soul or to our conscious, that is something that is bound to the different points of view.
Some of us believe in heaven or hell, others believe in returning to our home in the stars, others believe in a cyclical reincarnation based on the way one has lived his/her life... and there are so many points of view about what happens after.
For me, I just wait and see, but meanwhile, I wait, I try to make the most out of this life since it is the place where I can make the difference, and I can act on the direction it has to take.
I personally have no fear of dying, I embraced the concept a long time ago. I have found out that if you accept the fact that all of this is going to end and you keep it in mind, not like something to be afraid of, but something unavoidable, like the rise and set of the sun, or like the days going by and the growth of your hair, your life will get better.
You cannot stop it, so better live and deal with it; to be honest, the original quote from Mark Twain would be better rephrased this way: