I believe Muppet*Vision 3D at MGM is about 15 now, and it still packs them in and is certainly headed nowhere. If a show is inspired enough (and its star doesn't take a particular liking to 5 year old boys), it shouldn't need to leave. I can't imagine Mickey and Donald ever seeming stale. That would be a very sad day.
EDIT: Muppet*Vision 3D opened May 17, 1991, so it turns 15 in 10 months, and again, isn't headed anywhere.