We'll have to organize a post-ww2 berlin style airlift to support and supply Austin, though. A coworker of mine from there suggested at least one daily C130 fully loaded with kombucha.
And to be realistic, Texas absolutely can not secede by force, so it would have to be amicable with the Federal government, and in that case I dont know why they would be hostile to Americans traveling in their territory, as long as there arent any unescorted females, obviously.