I don't remember where I read this, but the SBA keeps track of small businesses. Their statistics show that 43% of small businesses closed by a disaster never re-open. That another 29% close within two years. I think that's 72%. I read this years before the 2005 hurricane debacle, and now the SBA's press releases all talk about how much better it will do next time. :-\ Cynics would say that the stats after Katrina and Wilma are so much worse that the SBA won't publish them. Others would say I just can't find them at http://www.sba.gov/

My suggestion instead of a generalized statistic on how long 'businesses of any time remain closed' is to look specifically at your situation. If you are in New Orleans, and you have a major hurricane, I'd say you should expect many, maybe most, businesses to fail to reopen. I live in the San Francisco Bay Area, and if we have "The Big One," I expect many businesses never to reopen. If it's a moderate earthquake, I expect some businesses to reopen as soon as we get power back, but I plan on a week without being able to buy anything anywhere.

If we have a major earthquake here, I expect people to move away, the town where I live not to be rebuilt in any reasonable time - another Katrina in New Orleans. I can't guess about your disaster scenario. If you live in a tornado belt, I'd guess it depends on the size of the town. Some are completely wiped out by major tornadoes - check your local news sources for what happened after such a disaster.