Throughout the coverage of the disaster that has befallen New Orleans, it seems one thing has been assumed throughout: the rebuilding of New Orleans. Much depends on how long it will take to get rid of the water, engage in massive repair and new construction, and how much of the city's tax base sticks around.
The reality is that the entire professional class or a large portion thereof will relocate because they are unable to wait for the new city to rise. Many businesses will take a hard look at the New Orleans operation and decide they can't let resources like fallow that long. Expect a major migration of many branch offices and probably some headquarters locations.
Even the poor citizens of the town whom we have seen engaged in remarkable suffering as all rescue efforts pale before their plight may never come back to town. As many of them are long term clients of government programs, they will probably have the option to spend time in ultra-ultilitarian state and federal camps or to resettle elsewhere with the help of social workers and/or family members in other cities.
Unless someone can show me otherwise, I don't think there should be any assumption that New Orleans is going to continue as a major metropolitan area in the United States. It may just be a ghost living a marginal existence. Galveston never truly recovered from the great hurricane that leveled the town and killed so many. New Orleans may not rise even so high as the old Wall Street of the West on the Texas coast.