Complex sentence: In 1964, Del Tredici met Aaron Copland at Tanglewood; they would be friends for the remainder of Copland's life, and his musical style remains an influence on Del Tredici.
Split into simpler sentences: In 1964, Del Tredici met Aaron Copland at Tanglewood. They remained friends for the remainder of Copland's life, and Copland's musical style remains an influence on Del Tredici.