What is the resolution?

This answer is not as straightforward as I would like it to be. The resolution depends on which version of the text that you are asking about. The original text of Hiroshima has four chapters. Hersey added chapter five 40 years later, and it briefly explores the six characters’ lives in the years after the bomb. Some of the characters do quite well, while others have long standing health issues as a result of radiation sickness.
If we are looking at Hersey's original text, the resolution is a bit more open-ended. Readers are told that each of the six characters are attempting to get on the road to recovery. It is a difficult road, fraught with health concerns and the deaths of friends and family members. Near the end of the chapter, readers get a paragraph that tells us that a year has passed since the bomb has dropped. Its opening sentence is a good resolution summary. The main characters have indeed survived the bomb, but their lives have been utterly destroyed.

A year after the bomb was dropped, Miss Sasaki was a cripple; Mrs. Nakamura was destitute; Father Kleinsorge was back in the hospital; Dr. Sasaki was not capable of the work he once could do; Dr. Fuji had lost the thirty-room hospital it took him many years to acquire, and had no prospects of rebuilding it; Mr. Tanimoto’s church had been ruined and he no longer had his exceptional vitality.