Logically speaking, we always must live in a world where past existential threats to humanity were avoided (including super-volcanoes, asteroids), but that says nothing about the possibility of future existential threats wiping out humanity.
Spoiler (including why it's related to your post) since I think it's easy to miss what this is: Vg'f n obk gung, jura bcrarq, qrfgeblf gur havirefr. Fvapr nccneragyl guvf obk yvirf va n znal-jbeyqf havirefr, vg'f onfvpnyyl n havirefr-fpnyr Dhnaghz Fhvpvqr qrivpr.
http://www.rot13.com/index.php , for your convenience.
And yes, I'm extrapolating a bit, but given the rest of the SCP-universe (inasmuch as there is a such a thing), it's a pretty reasonable conclusion. If it's wrong to you, well, it's right to me, Hail Fanon, All Hail Discordia.
http://www.amazon.com/Global-Catastrophic-Risks-Nick-Bostrom...
"In Global Catastrophic Risks 25 leading experts look at the gravest risks facing humanity in the 21st century, including asteroid impacts, gamma-ray bursts, Earth-based natural catastrophes, nuclear war, terrorism, global warming, biological weapons, totalitarianism, advanced nanotechnology, general artificial intelligence, and social collapse. The book also addresses over-arching issues - policy responses and methods for predicting and managing catastrophes. "
There's no reason a much diminished humanity concentrated in the southern hemisphere couldn't be marking the thirtieth anniversary of War Day today, if things had gone a bit differently.