The New Scientist reports that a supervolcano eruption may not be as world ending as we might fear.
New research by the University of Oxford suggests that cooling after the last major eruption - that of Toba 75000 years ago - would only be in the region of 1.5°C over a period of 20 to 30 years, although they do agree there might have been a 'short term period of severe cooling.' However, 'more dramatic dramatic dips have occurred without any major impact on humans.'
So apart from the devastating impact it would have on the modern economy it should be more or less business as usual for the human race.
Looks like Scavenge Skirmish Survive might have to go looking for a new Causus Exterminatus (?) to keep up its realistic bent...