I say let them go. Most red states -- i.e. those in the south -- are poor states. They get more money back from the federal government than they send to Washington. They'll be begging for reinstatement in less than a year.
New Orleans controls the outlet of the Mississippi river, and thus much of the production that flows out the US heartland, and they would be able to charge the US exorbitant transit rates or shut down traffic altogether.
The last battle of the War of 1812 was fought there for good reason, and holding the mouth of the Missisissippi was and is a strategic and economic necessity.