Many of gaming's biggest franchises have no endgame in mind—ask Nintendo when they'll stop making Mario games, for example, and you'll be laughed out of Kyoto. And the actual NFL is more likely to end before Madden ever does.
Assassin's Creed, though? The folks behind Ubisoft's longrunning action/adventure series say it'll end one day. They promise. Even though annualized releases are making Ubisoft a ton of money, and they've currently got at least three Assassin's Creeds in development, there's a finale in sight.