Neil Sedaka, one of pop's most enduring songwriters whose career extended from after World War II to the countercultural days of Elton John, has died, his family said Friday. Sedaka, the writer behind such songs as "Breaking Up is Hard to Do," "Love Will Keep Us Together" and dozens of other hits, was 86. His cause of death was not clear. "Our family is devastated by the sudden passing of our beloved husband, father and grandfather, Neil Sedaka," his family said in a statement to NBC News. Sedaka got his start in high school, performing with a doo-wop group, the Tokens, that recorded two hit singles. Collaboration with his young neighbor, Howard Greenfield, led to a songwriting partnership that lasted a half-century and resulted in 40 million records sold between 1959 and 1963, according to his official bio. Connie Francis recorded the duo's "Stupid Cupid," putting them on the music industry map in 1959. "Breaking Up is Hard to Do," from 1962, epitomized Sedaka's career at the time.…