In all fairness, there was never really much going on in that part of TX. Those towns are all Ag communities that were at their peak in the 1920s. They were on the southern edge of the dust bowl in the 1930s that pretty much killed off the small family farms and ranches. Those that survived eventually would fall victim to the farming crisis of the 1970s and early 80s. Now, most of the agriculture is corporate and the residents are now mostly low wage immigrant farm workers. This area has very little oil and gas as it is just outside of the productive parts of the Permian basin.
Texas is definitely dominated by the big urban areas, but there are some big success stories in rural Texas. Out in the Permian basin, Midland, Odessa, Lubbock, Big Spring, etc. are thriving (albeit in a very volatile boom/bust fashion depending on whether the Saudis open the spigots). In the Hill Country, retirees, second homes and tourism have communities like Wimberly, Fredericksburg, Dripping Springs and Brenham thriving with lots of service sector work and construction jobs. Even though TX wine is horrible, there are tons of new wineries around Fredericksburg. Out west around Big Bend, real estate in Marfa has become so expensive that locals cannot afford to live there.
Shale plays along the coastal bend, the panhandle, and east-northeast TX have helped rural communities like Athens, Victoria, and panhandle communities hold together and do about as well as any rural community in TX.