I'd like to know if there are records of people who went back to their country of origin or who left the USA to live elsewhere. In other words, ships' records in reverse.

Two reasons, the family story is that my grandfather went back to Italy to retrieve his son from a previous marriage during WWI. This was after my mother was born in the USA. My research shows this uncle was born here. So why did my grandfather go back? Was my uncle (his son) sent to Italy to live with relatives? I know who came here from ship's records but who went back to Italy? Who left this country, not just who entered?

Second reason is that I have my father's aunt and her family living in Philadelphia in the 1920s but by 1930 they totally disappeared from all records, even all the children. Did they leave the USA for Venezuela? I was told there was family who settled there.
Thank you for your help,
Alida Thorpe