Complex sentence: In 1857 Durov returned from Siberia, and in 1862 the ban on his literary activity was lifted, but, broken physically, he fell critically ill and died at the age of 54.
Split into simpler sentences: In 1857 Durov returned from Siberia, and the ban on his literary activity was lifted in 1862. But, broken physically by his long ordeal, he fell critically ill soon after and died at the age of 54.