What Bojack life in the end if he took responsibility and saved Sarah Lynn from her overdose
Even if he failed to save her, what happened if he went through with seriously making Ethan Around a success like Horsing Around and not repeat his mistake with Sarah Lynn to the child actor?
I’m uncomfortable with treating these two events equivalently. So I’ll address the Sarah Lynn question, and ignore the second part.
He would be able to live his life without thinking that he was probably responsible for someone’s death. Not just anyone, either: a friend, a colleague, a former lover, a sort of daughter figure. Someone whose life he made worse by being around her.
The difference it would have made was inconceivably huge.
Arguably, him failing to treat Horsin’ Around seriously indirectly led to the Sarah Lynn incident. OP isn’t suggesting they are equivalent at all, I think. They are linked in a way though.