Well there'd have to be something else to the game other than the aforementioned controversial events. They would probably have to use fictional locations and organisations as well.
For example, what would the player be doing in the Twin Towers? Just going to walk around as the building collapses then you die? Sure, that worked for CoD4 when you controlled a dying marine as he crawled around a town hit by a nuclear blast. But then you'd need other character to control. Or maybe you could be one of the firefighters in the Towers? There just isn't much action going on inside the Towers, but it's a great spectacle. Maybe you could be one of those people who jumped to their deaths. Slightly out of the ordinary for a game series where you spend 90% of your time shooting stuff.
And as for shooting Bin Laden, that's a lot easier to justify for a game where you usually shoot terrorists. But I doubt they would be able to even use his actual appearance and name, which defeats the point really.