I still haven't seen Season 9.
But, do you mean how should their story end in the show or how should their life end up if given a summary?
I personally would want something definitive yet not "ending."
Something where the story meant to be told was told. But, I'm a fan of something like Gravity Falls where it had a very bounded story. Began and ended. It had goals for the story it wanted to tell from the very beginning and ended that story line at the end of two seasons.
As for "summary of their lives" sorta ending, I mean, that's different. The show has continually felt like they added the "next logical step" in their story, whether it was what I felt was logical or not. It was still a good next step in their story. So, I don't really know where they end because the show just kept going. Which, is fine. It just makes it hard to really think of what the "end" would look like.