Complex sentence: After resigning from active work with the Party, she disappeared in 1937, never to be seen again, and is believed by several sources to have been abducted and murdered by a Soviet NKVD assassination squad.
Split into simpler sentences: After resigning from active work with the Party, she disappeared in 1937, never to be seen again. She is believed by several sources to have been abducted and murdered by a Soviet NKVD assassination squad.