Dallas is four hours away from Austin by car. It's not remotely in their catchment area.
May not be in their catching area directly, but the fact is the BoG has been all over Houston for decades now, it's just never quite managed to get done despite getting very close a couple of times. I don't see them quitting that pursuit now in favor of Austin; BoG head Jeremy Jacobs is
deadset on a team in Houston.
Oak View building an arena in Austin doesn't necessarily mean the NHL is going there unless you think Greenville, Lexington and Omaha are even potentially on the NHL's expansion radar as far as markets go. OVG builds and manages arenas in many sports, not all related to hockey; just because they're involved in building an arena does not make a market suddenly high-priority for an NHL team.
Houston is
already much larger than Austin and also growing quite rapidly. It has a building ready for NHL-quality hockey. Only thing you could
really say Austin has up on Houston is per-capita income, but we all know the NHL looks at market
size over market
capita income. Vegas is 84th in per-capita income, far worse than Houston's 68th.
And even if Buffalo moves (and that's an
ENORMOUS "IF"), it's not going to be to Houston because then they need to force another West team East to keep things evened out. The league doesn't want another Winnipeg-in-the-Southeast on their hands if they have to move Buffalo to Houston and then have them playing Toronto, Montreal and Boston regularly.
If they move the Sabres, it's to a location that stays East, one with a known and tolerated ownership group and ideally stays in the Atlantic on top of that. Now what location fits those criteria...