Many articles have been printed about former residents of New Orleans that have absolutely no intention of returning. Additionally, Louisiana has gone to extraordinary lengths to provide satellite voting sites and encourage absentee voting.
This just isn't rocket science. If you care enough about New Orleans and have intents on returning, you can make the effort to cast your vote. Quit whining and get on with your life. Current residents (I don't care where they came from) have a right to direct the future of their city by having an election.
Lather. Rinse. Repeat. :)
If it were up to Nagin, his power would continue until every resident was back living in NO (which will probably be never). In other words, he would be mayor for life. Works for him.