its is uncommon for authors in the 1800s to tie up all the loose ends of their stories at the end of their books. how does stowe wrap up the story of cassy's life?

Yes, stories in the 1800's were generally wrapped and tied for the readers; loose ends were not common. Cassy's story is wrapped up when she relates her background to George, and a woman, Madame de Thoux, overhears and reveals that she is George Harris's sister. It is then discovered that George Harris's wife, Eliza, is Cassy's daughter. Everything has come together.