Obviously most Americans wouldn’t be happy about it but I’ll bet they’d rather lose Texas than fight another civil war. Maybe, but the decision to fight wont be made by a vote of the general public. It will be made a president and/or congress. What politician wants to go down in history as one who permitted the dissolution of the USA? Answer: none. It would be political suicide. Therefore, he/they will decide to fight.
The decision wouldn't be anywhere near that clear cut. If he didn't have the public on his side, the decision to commit troops to kill Americans would be a
very difficult one. Doing so would have a huge downside, including a political downside (imagine images of US troops shooting down Texans). You can point to Waco and Ruby Ridge as precedents but those were police actions against a few fringe weirdos. We're talking about an actual war against an actual state. I find it easy to imagine that if the secession couldn't be stopped by means short of military action, the federal government would acquiesce and let it happen.
Keep in mind that the only thing modern Americans see as justifying the Civil War I was that it ended slavery. There would be no such clear moral justification for Civil War II. People would see their fellow Americans making a principled stand based on their sense of liberty, without a morally repugnant ulterior motive. Would they really be gung ho to send in the troops to stop that? I doubt it.