I actully read the title and thought it would be some rant about why COD isnt good, etc. but the OP does raise some interesting questions. people dont play COD for the characters, story, etc. they play it online, so imo its logical to assume that eventually someone else will come along and do it better.
however, imo its difficult to assume this because certain games have remained for decades, Mario being the obvious one.
but imo, based partly on what Scobes said as well, every COD game features the same online mode, like deathmatch, etc nothing is changed. the formula is the same. theres a 6 hour campaign, then as much online as you want. but can this last, imo it will last like other franchises have lasted, but some other game could come along and do it better, like Medal of Honor.
however the other thing is that some gamers will buy COD every year.