There is no official way of counting, but if you go by your previous post of upwards of 30,000 Bills fans in Nashville(roughly half the stadium), I'd be surprised if that number is topped in Vegas.
Don't get me wrong, it will be a great time, but I think the difficulty in getting tickets, will be a big detriment. I personally would not drop $1000-$1500(airfare, hotel and spending) to go all that way(from WNY) to watch the Bills on TV,