This is pretty simplistic. People walk around feeling fine and then find out they have Stage III or IV cancer. Things aren't always as they seem on the surface.
The vast majority of people that make interstate moves do so either because of household economics (job opportunity, housing costs, whatever) or proximity to family. It's not typically some dream of living in Texas - although, like others have mentioned, I do know a few transplants really into the cowboy cosplay bit so it is out there. The segment of the population that actually, consciously votes with their feet is very small because that generally requires a level of financial stability that most of the population doesn't have, and most people aren't willing to up and leave their family/friends, find a new job or close their business, or whatever the case may be to make a political point.
The growth machine - which at this point is self sustaining and plays a nontrivial role in the continued economic expansion of the state - will end for Texas at some point, just like it has elsewhere. At that point Texas is going to be left with a lot of very inefficient, expensive to maintain sprawl without the growth to pay for it. At some point, somewhere else is going to be the more cost effective and appealing option for businesses and citizens, and you'll see relocations out of Texas to hotspot X just like people once moved in droves from the east coast to the Rust Belt, and from EST and CST to California.
It will be interesting to see where the state goes from there. It has advantages California, the northeast (near endless supply of flat, buildable land across which to continuously sprawl), and the Rust Belt (international migration, diversified economy) didn't have when the growth cycle ended in those places. But it'll also face some unique challenges with climate change/water security (this is an issue for CA too), transition away from oil (no CR, it'll happen at some point even if it is literally pumping it all out of the ground), etc.