Generally speamibg, catastrophic thinkers DO NOT think that were all going to die at the same time. They think the world population will be hit with local natural disaster after local natural disaster where many will die. They believe that as our ability to respond to all these natural disasters decreases (from systemic fatigue), that the number of people who survive will decrease and the number who die from the fallout of them will increase. All of that until civilization collapses.