Dallas County is lost for the GOP, but that's not a big deal in and of itself. It doesn't do much good to shut a party out of a county when that county's population growth has been flat for the past decade or so and the counties surrounding it are exploding in population and are very favorable towards the GOP.
The Democrats are going to have to figure out a way to get more than 35% of the vote in the collar counties (Collin, Denton, Ellis, Rockwall, Johnson). Same story in other "sprawl counties" near Houston (Montgomery, Fort Bend, Brazoria) and Austin (Williamson).
About that.....