If Texas voted for a "texit" today, the federal government would respond by sicing the U.S. Army on them.
They could try but there are numerous military posts/bases located with the Texas Republic and I’m not so sure that all of those military folk would heed an Obama order at this point. Choose whom this day you will serve.
People are different today, who is going to join a fight against Texas?
The point is moot anyhow, if there was even the remote possibility of Texas or any other state actually succeeding in seceding, the dollar and economy would drop and our cities go up in flames so fast that no one would care.
It would be the opposite. If the feds shut down the army bases, air force bases, naval bases, depots it would be a large economic hit to the Texas economy.
Add to that the shut down of the US border patrol, NASA, federal court houses, the Mint, Pantex, etc, etc.
Texas has been thru this before during the 1990s and the Republic of Texas movement, when Bush was guv. That didn't turn out very well. The movement split into two groups and it became an internal war.
This is what no one is talking about with Brexit. Leaving EU will create a power vacuum and many conflicts will arise among those seeking to fill the vacuum.