One. Texas cannot secede from the United States legally. This means that there is only one method for Texas to secede and that is to murder everyone in Washington DC. That's it.

So knowing this, the United States in the event that Texas had thought it seceded from the United States would in turn end the lives of a whole lot of folks who supported this notion of secession. Of course there would be resistance to this whole dying idea from a lot of Texans and that would lead to a lot of US military also dying, not nearly anywhere near the amount of Texans dying, but a non-zero number none-the-less.

That's what a seceding Texas and the United States would have in store for itself. A lot of dead people. And that's the full extent of a Texas leaving the United States would look like. Dead people. Not riches, not freedom, not utopia, just dead people and lots of them. Because there's not a legal manner by which Texas can leave.

Two. So let's say Texas somehow finds out how to leave the United States. They have a pretty strong economy, but running yourself as a wholly independent nation is vastly different than running a State and right out the gate, there's a massive level of doubt that the Texas Legislature could pull off such a feat.

Additionally, the thing that triggered the first civil war would come back. The whole United States telling every nation on the planet Earth that they were not allowed to treat the Confederacy as an independent nation. It's really hard to conduct international trade of any sorts if zero people on the planet accept your currency. Now the TNM think they'll be able to score bilateral deals on their oil products. No one will trade with them at market rates, right out the gate that's the first thing the US will tell everyone. Texas in order to sell would need to sell to nations that weren't friendly to the US and those nations themselves would only do so at greatly reduced market rates. Nowhere near any kind of money for them to be a self sustaining nation.

Because on the International stage, if say Texas was trading with North Korea (for example), NK isn't going to hand Texas enough money (even if they had it, which they do not) to make Texas a threat to NK. That's being dumb. Internationally, you keep beholden nation, beholden. There are zero ways Texas does anything internationally because zero people will recognize their unit of money, which in turn means you cannot move goods outside your nation, which makes it very difficult to be an independent nation. Not to mention that given enough time, the US knows where the refineries are and hitting them with a missile is not some impossible task. That's part of the asymmetry of this whole thought experiment. Shooting one missile is very cheap for the US, rebuilding an entire oil industry complex is very expensive, especially for a nation that will be cut off from most of the metals and material require to rebuild. And even if they rebuilt it after X number of years, it still only requires a single missile to destroy it.

Even if Texas could, which they cannot, leave the US, there are zero benefits for them to do so and they would almost immediately be taken advantage of by foreign powers to a point that whatever economic benefit they have today, would be gone in a matter of years. The state has goodwill on the International stage but only by the virtue of being a US State. Most first world nations wouldn't trade with Texas just in principal and the US government would almost see to it that no nation on the planet traded with them. They do have a very strong domestic economy but it would stagnate easily two to five years in without international trade. Their median wage is just too low and their cost of living too high for them to coast on domestic consumption and production alone. Not to mention they would very likely be fighting a war with the US, which they would very likely be losing very badly.

They do not get to keep any airplane the US military bought and if they tried the US would just bomb it into dust. They don't get to keep airports Federal dollars bought, the US would pit the runways. They don't get to keep any ports facing the gulf, the US would set it on fire from their battleships. They don't get to keep any of it, they have to build it all back themselves, and if they try to keep it, we do the thing the US does best, destroy it completely with the idea that we'll just rebuild it back once we've killed everyone that's needing to die. Anyone who has studied the Reconstruction era already knows this.

But none of this matters because Texas cannot leave the United States, full stop.