I'll take it one by one:
The stories in Juan Bobo:Four Folktales from Puerto Rico went from morning to evening. So the book had to end with Juan Bobo going to bed.
Teresa grew out of her racism in In The Shade of the Níspero Tree. I knew her mother didn't. Still, unfortunately, I rewrote the ending with her mother changing her views. I regret it.
Biographies end with the death of their subjects--if they die. Even then I try to end my books with hope.
The Afterword of Poet and Politician from Puerto Rico: Don Luis Muñoz Marín begins with one of his quotes: "Gone to feed the roots of the gathering spring."
My biography about farmworker César Chávez was dictated to me (I prefer to think that he dictated it to me) so I just wrote it as told, including its ending.
I knew how to end my biography about muralist Diego Rivera. He was a storyteller so it had to end with a moral to his story.
My latest biography, Sonia Sotomayor: Supreme Court Justice, ended with her success!
I know how the novel I am writing now will end. Elisa won't become a nun!