My current theory is that its "every month population dies, and if everyone dies before situation ends, event ends" but I've heard multiple people had that happen while trying to aid them and on first time I got event I on whim decided to watch and learn and they went down to whole "age of warlords" and survived pandemic. So is it possible event is somehow bugged that trying to aid them makes situation worse? The one time I did try to aid them situation almost finished before everyone died(last event I got was about whether you reveal yourself or put more resources into staying secret when they try to hunt the "demons")