What would feel "wrong" would be to kill off the Avengers, not to mention some of the most popular and enduring heroes in the Marvel Universe in their own rights, after roughly a decade or so, thus denying future generations the opportunity to PARTICIPATE in an ongoing pop culture phenomenon instead of having to latch on to some previous generation's idea of what's cool.
Plus, it would undeniably, inevitably, and irrevocably flush Marvel once and for all down the bankruptcy toilet. Making an ongoing Avengers franchise makes Marvel not only the most profitable it's ever been, but also one of the most powerful and important movie studios on the planet. But *you* want them to close up shop after Avengers 3 just so you can keep the series under glass in your little museum to peruse at your leisure....?
Yeah...good luck.