Well if London were to get a casino I would assume it would be more like the one in Brantford (charity casino) opposed to something like Caesars Windsor. No hotel rooms or convention halls or anything of the like, just a gaming floor.
I doubt this will have much effect on Caesars Windsor. There are other casinos closer to London than Windsor (like Sarnia and Brantford) so I could see a minimal loss at these establishments.
Most Londoners who are going to Windsor or Niagara Falls to gamble are going for more of a vacation rather than a casino trip.
In addition, I took a look at the figures at the Western Fair slots. It generates over $100 million in revenue annually... That's insane, especially due to the fact that it isn't a casino. It blows other regional raceway track slot revenues out of the water.
(Plus I'm a sucker for Blackjack... I want tables here, although that may tempt me to play more
)