If a Republican wins the seat, it will likely be a Caucasian one. Unfortunately, as it stands, there is not a single solitary Republican interested in considering making a race, but there are tons of Democrats. Peggy Wilson could be one for us, but she seems more determined to run for Mayor instead. Nagin himself is mentioned as a potential candidate to replace Jefferson. If I had to bet at the moment, I would suspect a White Democrat tending towards the moderate-left of center would take the seat.
Since it's Louisiana, there will almost certainly be a run-off. If enough Democrats run it may allow the Republican to finish in the top-two and thus make the lower-turnout run-off. Even with so many New Orleans residents moving away, I still assume that blacks would be a majority of the electorate (after all, the Jefferson Parish districts in the CD are also heavily black and it's not like whites from the New Orleans area didn't move away as well). The only way that the GOP would have any chance at all of pulling off the upset would be with a black candidate; if a black Republican makes the run-off against a white liberal Democrat, our odds of winning would increase substantially, and even against a black Democrat we might have a chance. The problem is that I don't know any prominent black Republicans in the New Orleans area.