Here's a link to the Ethel Waters song referred to above. It's "Supper Time" written by Irving Berlin for a 1933 musical, "As Thousands Sing." The musical makes it clear that the father has been lynched. The song lyrics themselves don't tell you why he isn't coming home.
I don't remember just how old Judy Garland was when she died, but I'm sure it was considerably more than 15 years after The Wizard Of Oz was released (1939). When she did here most haunting rendition, I think, of "Over The Rainbow," sitting by the footlights of the stage, in her hobo costume and make-up, she must have been at least 35 to 40. Also, I could swear I saw her do duets with adult daughter Liza. Or did you mean that she died 15 years after you first heard her sing "Over The Rainbow?"