Complex sentence: Sielava had to leave Polotsk and died on 5 October 1655, when already (since 1653) the Greek-Catholic Church was in the resolute hands of Havryil Kolenda.
Split into simpler sentences: Sielava had to leave Polotsk and died on 5 October 1655. Since 1653 the Greek-Catholic Church was in the resolute hands of Havryil Kolenda.