I bet the league has a fallback (backup) in mind. Last call would be Portland in the event of a Vegas failure. And I think they're fine and dandy with that idea to suit their having first footing in the Sin City. Salt Lake City would reach out and might have a case in such an event. In the east, I feel Atlanta can be passed on for obvious and recent reasons, although I consider it a better alternative to Miami. To me, the capital of the south is a part-time hockey town (example articles for tag teams listed below).
Other drifting thoughts in the east are Milwaukee, Indianapolis, Cleveland and Cincinnati. But the thought of Portland not being the bride and rivalry of Seattle kind of rubs me wrong for the fleeting and luscious town of Las Vegas.
I suppose it isn't a slap enough about the face when it comes to hockey in Phoenix not becoming the West Coast Coyotes of Portland.
Midlakes Mustangs NHL Expansion Team