1)
Whom will Hashem have mercy on, and return them?
1.
Rashi: All [Yisrael's neighbors] were stricken close to the time of the Churban, and "I will return the captivity" applies to all of them, below (46:27, 48:47, 49:6).
2)
When will they return?
1.
Radak: When Yehudah and Binyamin returned from Galus Bavel, also [their neighbors] returned.