Complex sentence: They were imprisoned until 1788 when they were pardoned by Catherine due to Zorich's intervention and because of Stjepan's fame in western Europe, where he always glorified Russian empress and left for Arhangelsk, not to be mentioned again.
Split into simpler sentences: They were imprisoned until 1788 when they were pardoned by Catherine due to Zorich's intervention and because of Stjepan's fame in western Europe, where he always glorified Russian empress. Upon release they left for Arhangelsk, not to be mentioned again.