"Say to your brothers, 'My people!'{'Ammi' in Hebrew} And to your sisters, 'My loved one!'{'Ruhamah' in Hebrew}
There is no promise here, or anywhere else in the Bible, that Israel, in any sense of including the northern kingdom, would ever return to the promised land; and, although it is possibly true that a very few of the scattered ten tribes might have returned to Jerusalem following the Babylonian captivity, absolutely nothing that resembles a reunion of the two kingdoms appeared in that.  The "promised land" to which the true people of God will return has reference to the spiritual blessings "in Christ" and no reference whatever to any land promise.  "The reunion under a Davidic monarch" refers to the calling of both Jews (of both kingdoms) and Gentiles into the kingdom of Jesus Christ the Son of David  (Matthew 1:1)