They'd probably just air drop in, arrest Abbot and the rest of the central government, and declare martial law in Austin. With luck, they'd lock them up and put an appointed governor in his place. There's very little precedent here, so some kind of antebellum south repetition would be likely.
tl;dr, the feds would go full anti terrorist on the idiots in charge of the state.
It's definitely overvalued, but that's because it's currently valued as the most valuable automotive company on the planet.