Have to. There's no good reason for any residents to return at the moment - you can't get into the city or the other affected areas, and right now I-10 is desperately needed for emergency and relief vehicles.
I suspect that they're going to be using the "inherent runway" capability of the Eisenhower Interstate System designs in the area.
Water rising an inch every 5 mins at Tulane University per CNN. 17th St. Rd. and Canal levee is breeched per the police and they must evacuate the critical patients by helicopter. the water is too high for ambulances.