Complex sentence: In 1971 he became editor of "Analog Science Fiction" after John W. Campbell's death; after leaving "Analog," he went on to edit "Omni Magazine" during 1978-1982.
Split into simpler sentences: In 1971 he became editor of "Analog Science Fiction" after John W. Campbell's death. After leaving "Analog", he went on to edit "Omni" during 1978-1982.