Sad as it may sound COD may remain popular until an extremely bad cod is released or something better and popular replaces it.
Here is my Theory on why people play games like MW2:
MW2 isn't great nor is it Bad its a below average shooter riddled with game breaking issues and game balance issues everywhere. But why is there so many people playing online??
The reason is Simple: Because everyone else does, check your friends lists(PS3,360) you have an high chance that there is someone playing MW2.
The facts are is that because everyone plays it makes them put up with the issues and flaws because they want to play what there friends are. The only way to stop is too all think all at around the same time this game sucks. And thats what happened to me and my friends playing it. We got 2 months in after playing months of WAW, and i had enough and said this game sucked and sold it for BFBC2 and while they till played until they relied that it sucked and dont play no more.
But not everyone is going to do that especially the ones who dont understand whats bad and that there are much less frustrating and more enjoyable experiences. i guarantee that if you go into any game there would be one person that thinks this game sucks hard and they only play it because all there friends do.
So the only way COD is going to go away is there to be such an bad game that everyone hates it and i mean Worst than MW2 that the issues are more present then the gamebreaking ones.
But for the sake of gaming its self i hope this dies by next year because the FPS market is suffering and gaming its self because its tricking developers to make half ass games like MW2 but when they do they fail. most hope depends on Battlefield 3, or Activison f'ing up like they have done with most of there franchises
Of Course That's Just My Opinion, I Could Be Wrong