If Texas leaves the Union, that means the Tar Sands Pipeline is dead.
Texas also has water problems, so if the Union were to dam the rivers and streams feeding into Texas, Texas would be SOL. (EG you can't eat oil.)
Then there is the whole borders issue. All the money that keeps the Cartel from overrunning into Texas goes away, leaving the boarders wide open.
Lets see, biggest port, ok, your economy means getting those goods into the Union, which means the tariffs of the boarders coming out of Texas are
going to be huge. Airports, same issues, except now, instead of just the TSA going to Texas causing problems you likely have customs issues going out.
Not to mention The USA isn't likely to ship you any new fuel for the reactors in Texas, so there goes a lot of your power, but that's ok, Texas
won't have any EPA so the kids there can drink fouled/poisoned water and breath filthy air.
With out going into the social/religious aspects of all the worst kinds coming back into vogue....
I'd give the odds of Texas surviving the succession, as marginal at best.
M.