Everything is legal if both sides agree. Texas has always been too valuable to lose. Louisiana, not so much.
Think about it, who would bitch if New Mexico left?
Remove the port of New Orleans from the Mississippi River, as well as all of the offshore drilling and rethink your stupidity. There is nothing in Texas, or any other state that comes close to providing the economic benefits of having a major river system served close to the Gulf of Mexico by an international port. Two-thirds of the interior of this country DEPEND on being able to cheaply ship and receive goods from the rest of the world. in addition, Louisiana has sacrificed it's coast lands so unappreciative folks like you can drive a car to work and live in a modern world.