Because the fact is Texas is not Virginia , it is not a state that the GOP can make up for losing as without TX the GOP dont have a path to 270. Due to that I think if Texas Flips, it will set of a new realignment and within 8-12 years the entire map will look so remarkably different that we wont be able to recognize today. Many trends we are seeing today will reverse, or there may be trends we don't even think about happening which will happen.
If Trump wins in 2020, this will probably happen and by 2032 or 2036 the map will be unrecognizable to today. On the other hand if Trump loses by even a 2012 style Romney margin EC wise then , I think the previous alignment may return (not pre 2008 but pre 2016 alignment)
Why would this happen though? What does Texas have to do with it? Is it the idea that losing Texas will force Republicans to totally change their strategy and policies? That would take a lot longer than a decade to yield results, and generally voters are a lot less focused on concrete policy than people like to think. If they were, Trump supporters would be holding dear leader's feet to the fire more often. Instead, they just go along with whatever he wants.