During the years that Israel was split into the 10 northern tribes (Israel) and the two southern tribes (Judah) the scriptures tell us that some people from the ten tribes migrated to Judah to worship God in his temple. And some of the Judahites (Jews) migrated into Israel to get away from the worship of the true God. So there have always been representatives of all tribes in both groups. After the Babylonian exile of Judah, the Jews under Ezra when back to the land of Israel and rebuilt the holy temple.

So what does history record happened to the majority of the 10 lost tribes?

• Josephus Ant 11.5.2 - there are only two tribes are under Roman rule.
• 2 Esdras 13.40 - They went to a place called to Arsereth,  area north of the Black Sea. 
• Commodianus  42 - This early church father adds a complete chapter on the lost tribes.
• More to come...
  

Theories:

1. They became the Celts and migrated to Europe 
2. They intermingled with the Chinese.
3. There are no lost tribes, they all went back to Israel
4. They are still lost, know one knows where they are, they may not even know who they really are.