The Santa Clara thing was always weird. In any conversation that I've had with someone who has attended a non-49ers game there (P12 Championship, Super Bowl, this year's NC Game), the attendee has always more or less come to the same conclusion: there's no "there" there. There's no nightlife, no major attractions, hotels are stupid expensive because "Bay Area", and if you get some sort of competing event in the Bay Area with corporate attendees it gets even more expensive.Maybe a full stadium trumps all these? I have no problem with a Vegas championship game, as long as the stadium is full. I'll guess they'll get more fans in the seats in Vegas than Santa Clara.
Compare that with Vegas and it's a no brainer. As a college kid, I could scrape and afford a (very) economical trip to LV, but there is no way I could have afforded to go to the Bay Area. Las Vegas flights are relatively cheap for the entire footprint, and it's less than a 12 hour drive for all but 4 schools. There's also more than 150K hotel rooms in Vegas so rooms are never is too expensive. Additionally, it's a vacation destination because there's a ton of stuff to do there. It's much more attractive to most people to spend a weekend in Vegas than it is to spend a weekend in Santa Clara.
I think we'd see a much higher attendance in Vegas than the P12 ever had in Santa Clara.