Complex sentence: The choir was taken over by George Smith who conducted the Choir for some 18 years and on his retirement for health reasons the Choir was successfully conducted by Roger Wills until his retirement in 2008.
Split into simpler sentences: The choir was taken over by George Smith, who conducted the Choir for 18 years. Upon his retirement for health reasons the Choir was successfully conducted by Roger Wills until his retirement in 2008.