I like the idea that divergent timelines can merge back together if differences aren’t significant. Say you had the choice of sausage or bacon for breakfast. That creates two timelines, but if you forget your choice a week later then the two flow back together. Breaks only occur when different choices create real and lasting differences.
That was kind of the case in BTTF. Marty made some arguably major changes in history, only to make relatively minor changes in the future. Despite radically changing the arc of his father’s career, his family still had the same siblings (just less losery) and lived in the same house.
There’s always the “many worlds” theory. You can change history, but you can’t change your history. Basically, any change creates a new and independent timeline. Due to chaotic effects, your mere presence in the past inevitably creates changes, so you can never travel to your own past.
I still have my Pooh-bear, complete with music box. Even if I did replace his red vest with a blue plaid smock at some point.