In 2 Kings 17:6, 18:11 and the parallel passage in 1 Chronicles 5:26, nothing is said about the deportation being partial, and there is no indication in the Bible that any significant number of the deportees later returned. An exception is mentioned in 2 Kings 17:24ff: When the Assyrians settled other tribes in that land, they found the land hostile to them, so one of the exiled priests was allowed to come back and teach them the local (i.e. Israelite) religion.
There are many legends about what happened to the "Ten Lost Tribes"; for a summary see Encyclopedia Judaica, vol.15, cols.1003-1006. But there is no solid evidence of any existing group being descended from them; they have left no indisputable traces. There were Jewish groups in Ethiopia that apparently did go back to First Temple times, and probably had connections with the tribe of Dan. The groups that have been found in Mexico, India, etc. are of less certain origins; they may be of Jewish descent, but it isn't possible to associate them with any specific tribe.
The Tannaim disagreed as to whether the Ten Tribes will eventually return; see Mishnah Sanhedrin 10:3. If we accept Rabbi Akiva's view, we must conclude that they are permanently lost; but many Tannaim did not accept this view (see Talmud Sanhedrin 110b).
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