Whoa whoa whoa, let's slow down a bit. Modern Warfare 2 only came out 3 weeks ago and now you're already asking about Modern Warfare 3? You guys are rushing ahead of the public again. It's just like when Map Pack 2 came out, you guys were discussing Map Pack 3 and some people even Map Pack 4 just 2 days after MP2 came out!
But if you really want my opinion, I think they will. Considering the fact that Modern Warfare was the biggest success of the CoD series, and Modern Warfare 2 was apparantly named "Most Anticipated Game of the Century". If it's money that IW want, MW3 will exist. If it's an angry mob of nerds burning down the company they want, they can just do what Treyarch did and completely rear-end all of there fans.