Complex sentence: Southworth was a highly respected leader of the Leiden group who would die in 1621/22, with his wife Alice then leaving for Plymouth Colony on the Anne in 1623 to become the wife of widower William Bradford.
Split into simpler sentences: Southworth was a highly respected leader of the Leiden group who died in 1621/22. His widow Alice then left for Plymouth Colony on the Anne in 1623 to become the wife of widower William Bradford.