what does sam do and what happens to him

In Ruth's family, however, Tateh was unbearable, and Sam, a quiet, submissive shadow, worked like a slave in the store. He ran away in 1934 at the age of 15 to Chicago, and wrote a letter home saying he had a job working in a store there. He never came back. Ruth only later learned that he had joined the army and had been killed during World War II.