A tribe is far too big to lose, of course. In 722 B.C. the Assyrians conquered the kingdom of Israel, which was the ten northern tribes (the other two tribes formed the kingdom of Judah) (2 Kings 17).
Many of the people were deported, and foreigners were settled in Israel. The deported Israelites were dispersed around the Assyrian Empire, most of them never to return.
They were probably absorbed into the lands they settled in, but many legends have sprung up around the “ten lost tribes.” Mormons believe that “lost tribes” settled America.