I think what we saw in TX this year was akin to what we saw in GA in 2008, where it suddenly lurched pretty substantially toward the Democrats but meandered a bit back in the GOP's direction before slowly continuing to inch toward its future reality. Basically, in both cases we saw Democrats in these states capitalize on what would have otherwise been multiple cycles' worth of gains in one cycle, with an obvious correction following that. As such, it could be another ten years or more before Democrats outright win there.
I definitely wouldn't describe TX as a purple state just yet: let's remember that despite all of the straight-D voters Beto turned out, Abbott still won the Governor's race by more than Rick Perry did in 2010. That underlines just how many voters mainly didn't like Cruz and/or aren't yet willing to punish the GOP up and down the ballot for the sake of Trump.
Governor's races don't match up much with national politics. It wasn't just Cruz and Beto, but the Democrats also only lost the House vote by about 3% too.
I'd say it's a case of a reasonably popular governor being able to to distance himself from the national environment, and seeing the state trend toward Democrats again otherwise.
