1. We cannot predict when we are going to die, unless we are really advanced practitioners. If it is going to happen, it will happen and no amount of worrying will stop it from happening. Even tulkus like the 11th and 12th Karmapa, Jamgon Kongtrul Rinpoche died young. If it is going to happen, might as well remain calm and recite good aspiration prayers.
2. However, if we are Buddhists, even if things like sicknesses or death or what other people may term as bad things occur, we always have methods of perceiving them as positive.
We have gone for so many pilgrimages and we do so many prayers everyday. Even if we die, in our mindstream, we have firmly planted the seed to 1) gain enlightenment if we have had a good practice and can recognize the clear light at death, 2) be reborn in dewachen (if we can recollect Od Pag Med and Chenrezig at the point of death), 3) have a good rebirth if instead make the strong wish to do so.
3. If we are very worried or nervous, it will have a negative effect of causing rebirth in the lower realm. It is like failing the examination we have prepared everyday for. Our aim is to gain enlightenment to liberate all sentient beings. For that aim, we train our mind everyday, to be very familiar with the Buddhist concepts, so we can deal with whatever happens, calmly, peacefully and in a Dharma way. "Nga na na na te na wei ga" and "Nga shi na shi te shi wei ga". If I am sick, I have the happiness of being sick. If I die, I have the happiness of dying. It is the same. You may be young, and you have many things you want to do that you have not done yet. But you can always continue your works in your next life. Buddhists should not view that life and death has any difference, both are bardos.
4. If you feel regret that you cannot finish what you want to do in this life, then all the more it gives you motivation to put in a lot of effort to finish what you want to do. So it is not necessarily a bad thing. Now you know death is so close to us, I am sure you will put in even more effort. Even if you really cannot finish it, no problem, you can continue it if you make the wish for a good human rebirth.
5. The point of death is a big opportunity, a wonderful one where we can gain enlightenment, just by recognizing the light or the deity. So it is a joyous occasion.
6. Have trust in the practice. If you have done the long life practice, it would have extended your life unless you have some ripened karma to pay back, which you cannot control anyway.
I am also hoping I can remember what I am writing now at my own point of death. Honestly this time, if the bus or plane were to have crashed, I don't think I would have felt fear or worry, because this was a time when I did practice everyday and I was so full of good aspirations. But I don't know about the future, I hope I can maintain things this way.
I have actually had quite a few near death experiences, maybe that is why I am more relaxed now in dangerous situations and also why I place so much emphasis in learning the Dharma. I was nearly hit by a car when I was young and playing on the road, I nearly drowned twice in a pool, last year I nearly fell down a cliff when we came back from Yolmo because the bus was close to knocking me down. It is really a blessing to still be alive and be able to finish my 3 month retreat/ study in Nepal and meet with so many Dharma friends.