It took the UK years to figure out how to make Brexit actually work, and it's a work in progress. I wonder how Texas will be able to pull this off. States are so connected to the federal government economically that' it's a big effor to unravel all that.
I think it's more, the powers that be don't want to make brexit work, and have been dragging their feet for years.
On the topic of fedgov gibs, you have a point that they will probably cut off all federal bennies and grants, and that is a problem. But an even bigger problem is the fedgov will lose all that revenue from Texas. Then the issue becomes would Texans have more to gain from no longer having to pay federal taxes than they would lose from not getting any more federal gibs. Older people on fixed incomes would probably have more to lose, while younger people likely have more to gain, not least of which being the issue of whether social security will even be solvent by the time they are old enough to collect it.
Then you have the non-rational factors. It's an open secret that the rulers in DC hate people in red states. They love nothing more than to lord it over the rest of us, and impose their values and ideology on us. They also just love power. They will not willingly relinquish power, and they will not willingly back off and leave the people they hate alone. So they will keep antagonizing the flyover country people. When flyover country has had enough and is willing to break away, damn the consequences, DC will go to war to try and stop them. Why do you think they are so adamant about marginalizing normal, patriotic, Christian White men in the military? They know that degenerates and imported peoples with no connection to legacy Americans will have no problem firing on them.
Of course China and Russia are probably laughing at us right now...