New Orleans should not suffer a fate any different than Times Beach, Missouri or Valmeyer, Illinois, or any of a myriad of small towns and settlements built too closely to the Mississippi and it's tributaries over the centuries.
Preserve the "Crescent", if you really gotta' do that, but relocate everybody and everything. Bring in the gators and some subtropical crocidiles. Build a big fence. Nature will take care of the rest.
To expand on your theme, preserve the French Quarter and everything bounded by 90, I10 and that other road I640[?}. That makes a nice boundry of high ground, was not flooded and should be easily restored.
Then let the swamp take the rest. Offer air boat tours to themed names like Cajun Land ["See actual Cajuns catch crawfish and cook over real wood fires!], Pirate Cove ["Hunt for LaFite's buried treasure!"] and, of course, The Battle of New Orleans interactive site. There might even be room for a dinosaur theme area....
They might want to consider Disney for a job that size and scope.
Might even run monorails out to 'em.