It's not at the end of its life but it's at end of its creativity. They found a pattern that they think will work forever (or at least this expansion) and I doubt they'll change it unless things go very sour. How confident they are that people won't get bored of the same formula for all future content, time will tell. Judging by the forums, there are a lot of addicts who'll consider any checklist worth doing as long as SE gives it to them, regardelss of its content. As long as those people can keep the game alive, it'll go on to fund SE's other projects.