I think that if Texas did this, against the Feds and the Feds went after them, I would think that other states would join them. Then you could have another civil war.
If Texas went out—other states would join them. This would happen only if the President disregarded the US Constitution. Then Texas and others could form a new nation—The Constitutional States of America-—using the old USA Constitution around the Government. This would mean Civil War—if Texas seized nuclear arms and threaten to destroy New York or Washington-—It may end as soon as it starts. In any case—the USA would cease to exist.