Well, keep in mind that the petro chemical plants are spread out over nearly 100 miles from Baton Rouge to southeast of NO, and it is unlikely that the storm will run up the river. It also would have to hit somewhere within about a 50-70 radius to create the catastrophic flooding case filling the NO bowl. Most of the plants also are within levees creating a bowl, but few of them have the convergence of problems that make NO so vulnerable. There is a big difference between damage and destruction, and most of these plants could probably be down for just weeks, rather than months for the city. It is amazing what a critical industry can do to get capacity back up. A city is far more complicated.
But your point of a worst case having national implications is well taken. Would be a much bigger evaporation of wealth and disruption than 9/11.
This is turning into a complete nightmare.