Bit off topic as it's not net.levees but i think that given that NO didn't take the full hit of hurricane force winds the levees will hold, just, but there may be some overtopping, and certainly some flooding in central NO due to heavy rain.
The downside of this is that when people return to a larely intact city (a good thing) they will question why they evacuated and may not be so eager too next time (a bad thing).
There is a lot of tornado activity east of NO at the moment, if Gus is taking a shifty to the west this could be bad news.