I just think you have to not think on it too much, theres no line you can draw once you start that thought process, if WW3 doesnt get us, climate change will, if climate change doesnt get us, a supervolcano like Yellowstone erupting will, if a supervolcano doesnt get us a 9.9 Richter earthquake will, if a 9.9 earthquake doesnt get us, an asteroid impact will, if an asteroid impact doesnt get us, a deadly disease will, if a deadly disease doesnt get us an alien invasion will. The list just goes on, you could cripple any chance of advancement or enjoyment of your life if you take that thought line. You just have to accept that we, as individuals and as a species, are transient. We come, we exist, we die and the next one comes along to take our place. All you can do is live your life to the fullest.