Tesla sells a lot of vehicles in Texas. We live in the Houston area - and were one of the first Model S owners since early 2013. In the early days, there were so few Model S cars that we were getting stopped coming out of restaurants and people frequently taking pictures of our car at stop lights.
Today, things are much different - we usually see many S/3/X vehicles when driving around town.
The lack of direct sales is no big deal. For our first purchase, it was more challenging because the nearest open Service Center was in Denver, so Tesla had UPS ship our S to our front door. Once the Service Centers were open, Tesla has improved the delivery process so it's not that different from purchasing from another dealership, except requiring us to pay for the vehicle (by transferring funds using our bank's website or smartphone app) prior to taking possession.
As for service, we've always had great response from the Service Centers and haven't noticed any issues because Tesla centralizes the service center support in California. And even if the talked-about bill passes (low probability) and it does impact Tesla's ability to operate Service Centers (which the bill's author disputes), it shouldn't be too difficult for Tesla to work around the restrictions.
If you're visiting Texas with a Tesla - you shouldn't have any problems if you need service (though Texas is a big state, and if you aren't in one of the large cities, you could have a long drive to the nearest service centers).