What do you mean the city still stands a chance? They need to rescue those they can and when this is over they should NOT rebuild that city. Basically there is nothing left of it except the French Quarter. That ought to be made into a Historic District and the rest allowed to return to wetlands. If they rebuild NO, it should be someplace else.
A rough rule of thumb is that in well-evacuated areas, 10% stayed, either because they were considered to be essential personnel or "I'm a divorced mom on duty and my kids won't be safe in the shelters", or because they were totally clueless and looked only at the way the storm was tracking earlier in the weekend (headed for Louisiana's instep).
For e.g. Gulfport, this would give 20000 stayers. If even only 10% of them lived in the surge zone....
Repeat up and down the coast.