The average value of a possible timespan between yellowstone eruptions, which varies between 600.000 to 730.00 years, is almost useless. 3 dates do not enable a reliable prediction at all (just some authors and journalists imply an accuracy anyway).
Anyway, a caldera-forming eruption is the most improbable scenario. The most probable scenario is hydrothermal eruptions, followed by small lava eruptions, so say serious geologists.
But even if a big caldera-forming eruption should take place, I doubt that this would be the end of modern civilization on the whole. But it certainly would be critical for emerging countries and third world countries, although a possible global average temperature decrease is nothing more than theory for now (a climate change is always assumed to be bad anyway, no matter if it's about warming or cooling). I think that modern civilization even will be the reason why a lot of people would survive. I don't see any reason for no electricity, no Internet/TV and no food. Certain men can, and will survive some surreal scenarios.
No past yellowstone eruption, nor any other event in Earth's history, was able to prevent the globe being colonized by humans and modern civilizations like it is the case at present. This shows how flexible the nature really is (and modern men even more).
These days people believe in the ability to colonize the Universe. People even believe in the ability to control the Earth's climate. But people don't believe in a survival in event of a yellowstone eruption. Funny.
