Well, they were charging a ridiculous amount for that one game (something like $200 a ticket even for average seats) because they guaranteed a certain amount of money to the Bills. It wasn't sold out because people in Toronto don't have $800 to bring the family to one game.
If Toronto was in the US, it would be the fourth largest city. I bet that a non-sold out game in Toronto generates more revenue than a typical game in Orchard Park. It may not be an overnight thing, but Toronto could be a major NFL town over time.
The fact is that the Bills' days in Buffalo are probably numbered. The Bills' average ticket price (about $51) is the lowest in the NFL (and they can't sell out every game because the economy can't support it) and more than half of what the Pats charge per ticket (about $121). It will be impossible for the Bills to stay in Buffalo whether they go to Toronto or Los Angeles or somewhere else. The local economy cannot support an NFL team going forward especially if their is no salary cap. Well, they could survive like teams like the Pirates survive in MLB baseball basically being eliminated from playoff contention before the season even starts because their entire payroll couldn't even fund the Red Sox's infield. I don't think the NFL wants a MLB system where there is at least 5 or 6 teams that have absolutely no shot every year and they will force small market teams to relocate even if it is out of the country to avoid this especially if there is no cap.
The Bills average more than 70,000 a game, and they do sellout now. The stadium is perhaps too large, but 70,000 a game ain't bad. Buffalo is top 10 in attendance. If you look at income, they are not at the bottom. Their gross revenues are small, but since Ralph pays nothing for a stadium, gets tax money for its upkeep, they actually do well.
I agree with you that lack of a salary cap will kill Buffalo in the future, but that's a problem for the NFL. You have 32 franchises, some franchises are worse off than Buffalo--Jacksonville, Oakland, Cincinnati, etc.
You're going to find places for these teams to MOVE to. Maybe Toronto is one, though I have my doubts about a stadium that seats 50k MAX. More like in the 40k range.
What about the other teams? Where are they moving to? I think the NFL will have to get used to parity being a thing of the past, because the mega earning teams are now well beyond the half of the league.
Within 45 miles of downtown Buffalo, you still have over 3 million people living here. This doesn't include ANY of the Toronto metro area. That's still a substantial population base.