Many times, in my career while negotiating something with another party I've said, "Let's get this fixed, it won't mean much to either of us in 50 years and in 100 nobody will remember either of us." I've managed to solve some pretty hairy problems saying that, the other party usually pauses and realizes the futility of our disagreement and we work something out. Call me morbid but I started saying that when I was 18…
It's not morbid, but sensible. No-one gets out of life alive. An unexpected death in my immediate family several years ago helped me realize how underprepared most of us are for death; for all the people and living things around us to die. Rather than be caught surprised, I've tried to remember that life can end in any moment, and it's best to make the most of things (and borrowed atoms, as you say) while you can.
On the one hand, some one realizing the seeming meaninglessness of existence is banal. This is well trod ground for many after all. But on the other hand it's also a an xkcd 1053[1] privilege to be a part of the authors epiphany.
Personally, for myself, the question of 'what legacy shall I leave?' resulted in finally settling down and having children of my own. I felt like I received an immense gift of a kind, warm, and loving home. I seek to continue that legacy with my own family. Because in the end, that's all most can hope to do; be a positive influence on the generations to come.