Tejas is NOT Midwest, are you fucking kidding me? It is a South or Gulf state.
You probably never been there/here.
It is a historical oddity that there is only one country in all this space here (US), though.
In a split up situation, Texas would do better than many coastal states, sans California and possibly WA or NY.
Outside the cities yeah it's pretty similar in terms of people/attitude. Yes, Texas does have its own power grid and yes they do have some diversification and yes they may survive a bit better. But in a splitup they would wind up subsidizing the crap that is known as the rest of the midwest.
(And yes, I've been down there many times. Riverwalk is nice, the roads are empty as fuck, Dallas is a bit too big, and Austin is just weird)