Rainbow Zebra
Satsu runs away with that boy (forget his name) from her village. Its in the book.
I think Hatsumomo either found koichi and ran away or became a prostitute or killed herself.
It's been a long time since I read the book or even since I saw the movie, so please bear with me. Satsu was the sister sold into prostitution, right? I do not remember if the book said what ultimately became of her or not. The movie certainly didn't say. She ran away with a boy, but beyond that it is up to our imaginations. As a former prostitute, she would not have been considered proper material for a wife, especially in those days, so that has to be considered as well.
As for Hatsumomo, it was only in the movie that she burned down the house and fled into obscurity. In the book, if memory serves me, she becfame increasingly psychotic and finally bit a customer she didn't like. This was professional suicide, of course, and she fell increasingly out of favor with everyone. I don't remember her trying to burn anything down, but it does seem like she was forced to leave and rumor had it that she became a prostitute, but Sayuri wasn't sure, herself.
The real geisha that Hatsumomo was based on was in fact the heroine's biological sister who had left to get married, then found herself having to return to the Okiya, but in a position subserviant to her younger sister (the character Sayuri was based on). Unlike in "Memoirs...", however, the two women sorted out their differences and became true sisters and friends again. Correct me if I am wrong, but that's how i remember reading the story.