Levees have a lot to do with the sinking state. The silt is channeled out into the gulf far enough that it does not add to the delta. The river is prevented from changing course which it did periodically in days of yore and distributed the silt better and built up the coast. Loss of NO would put a terrific crimp in the national economy way beyond the loss of oil rigs and refineries as it is the port that sends out the products of the entire Mississippi Basin which is the entire midwest. Transport to NO by water is easy and much cheaper than transport by truck and train to the West Coast or Norfolk or New York.
Move the port upriver.