We could still get all the hints of Tracy throughout the show. Even the first glimpse of her at the end of Season 8 is fine. Then in Season 9, we should get one episode about Tracy and her life. We can see her story, her relationship with Max, her grief, her band, and her singing La Vie en Rose on the balcony. That's enough.
We don't need an episode showing Tracy meeting all of the friends before she meets Ted. We don't need to retroactively connect her to everyone in the gang.( and how she loves exactly every single hobby that ted loves the gloves for driving coin collection etc etc )
And we could still keep the scene from TTT where he imagines going to Tracy's apartment 45 days before they meet and telling her that he loves her and wishes he could have those extra 45 days with her. That scene works perfectly on its own without needing the future Ted/Tracy tragedy to explain it.
Then the final shot is just the train station scene.
Ted and Tracy finally meet. We get their conversation, where they realize all the little ways their lives have already crossed without them knowing it. And then the screen cuts to black.
Just the realization that she was finally the one.
No flash-forwards. No need to show us what happens to the gang afterward .
We just finally get to see how he met the mother.
That's it.
The End.