“Now these are the singers, the heads of the ancestral houses of the Levites, living in the chambers of the temple free from other service, for they were on duty day and night. These were heads of ancestral houses of the Levites, according to their generations. These leaders lived in Jerusalem.”
The singers or cantors returned. Apparently this was also a hereditary role. I am not sure why they had to be on duty day and night unless it is a reference to what preceded. Some of these Levites may have remained in Jerusalem, especially if they were not leaders or rich. Others may have returned.