If you plan on staying through Mardi Gras Day,Carnival has a ship that presently leaves on Monday & Thursday. The Thursday after Mardi Gras.
Or, check with NCL & RCCL to see if they will bring any ships back to New Orleans 2005.
Don't delay,hotels at Mardi Gras are at a premium. Usually a minimum stay is required.
I live 7 miles from New Orleans. We're cruising on the Conquest Mardi Gras week.