The government will help rebuild. Companies in the WTC were covered by insurance, and if not, the government will help them rebuild. Ever hear of FEMA? They will step in and provide enough money to make sure everything goes back to the way it was before (as far as the companies are concerned). The gov will borrow money from the citizens, and eventually pay it back (ever heard of savings bonds?) Everything will be OK. There will be no depression. The economy will be fine, and it will be business as usually before we know it. However, NO ONE will forget what happened yesterday.
Ryan