http://sacred-texts.com/jud/josephus/ant-11.htm they were not lost from view see chapter5.2,,,,
the link says...
"wherefore there are but two tribes in Asia and Europe subject to the Iomans,
while the ten tribes are beyond Euphrates till now, and are an immense multitude,
and not to be estimated by numbers."
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These two groups, the no. kingdom of Israel, and the so kingdom of Judah,
did not come back together then .
1) In 721-718 b.c. Israel began to be “carried away out of their own land to Assyria” (2 Kings 17:23).
They were soon all removed—completely. “[T]here was none left but the tribe of Judah only”
(verse 18). Judah, only, remained.
2) More than 130 years later, Nebuchadnezzar of Babylon carried the Jews—Judah—who only
remained in Palestine away to Babylon. So none of the house of Israel dwelt in Palestine at the
time of this captivity of Judah.
3) Those who returned to Palestine to rebuild the temple and restore worship 70 years after Judah’s
captivity were all of the house of Judah—all Jews—all of those whom Nebuchadnezzar had carried
away. They returned again “unto Jerusalem and Judah, every one unto his city” (Ezra 2:1).
Only those of the tribe of Judah, together with remnants of Benjamin and Levi, who constituted
the house of Judah, returned at that time. “Then rose up the chief of the fathers of Judah and
Benjamin, and the priests, and the Levites?…” (Ezra 1:5).
The current nation of Israel is a misnomer, They are of the tribes of Judah and Benjamin.