The idea that the nation of Israel "lost" ten of its 12 tribes thanks to the Assyrians is one that gets a lot of play in literature of The Da Vinci Code variety. But does it have any basis in fact?
Richard Bauckham in Gospel Women [79ff], as part of a study on Anna the Asherite in Luke, answers that question with a resounding no. Let's have a look at his evidence.
The core refutation of all "lost tribes" theories is simple: There is no indication that the Jews ever considered the "lost" tribes to be "lost". Indeed all of the evidence suggests that members of the tribes continued to be able to be identified:
In addition to Anna being identified with Asher, 2 Chr. 30:11 indicates that Asherites still lived in Galilee, even after the deportation to Assyria.
Josephus (Ant. 11.131-33) reports that when the Jews were permitted by the Persians to return from exile, a copy of the decree was sent also to Jewish "compatriots" who lived where they did because of the Assyrian deportation. However, he reports that "the Israelites as a whole remained in that country", with "countless myraids" living beyond the Euphrates in his day.
Josephus' point is confirmed by Lives of the Prophets 3:17, a writing of the first century which says, "the people would not return to the its land but would be in Media until the consummation of their error."
Likewise, 2 Baruch 77:22 says that the other tribes were "over the breadth of the many waters of the Euphrates."
Acts 2:9, as well as other secular texts (m. Sheq. 3:4; Philo, Leg. ad Gai. 316), say Jews from Media continued to attend festivals and Jerusalem and send their temple tax. In addition, rabbis sent circulars (letters) which included an address to the exiles in Media.
Bauckham also notes bits of evidence allegedly showing the "loss" of the tribes:
4 Ezra 13 -- it is from the apocalyptic work that much speculation about the tribes being "lost" derives. In this chapter, the Messiah destroys his Gentile enemies and then calls for the "peaceful" exiles to return home. Bauckham argues that 4 Ezra is a counter to beliefs such as are found in the Qumran War Scroll that all 12 tribes will take part in a war against the Gentiles. But 4 Ezra goes on to say (later echoed by the Christian writer Commodian) that the king of Assyria deported the tribes to "another land" and that the tribes then decided to "go to a more distant region, where no human beings had ever lived", a place a year and a half away called Azareth. Bauckham believes that this statement comes of two factors: 1) After the destruction of Jerusalem in 70, contact between the Median exiles and Palestine became less frequent, so that they could "more easily fade from view" (though Bauckham acknowledges that the tradition may pre-date 70); 2) 4 Ezra made this claim based on a midrashic exegesis of the Abrahamic promise that Jewish descendants would become incredibly numerous, and deduced by their own logic that the only way the people could have become so numerous (ad also, numerous enough to defeat the Gentiles) was to expand into unknown territory, not limited to the communities still present in Media.
m Sanh. 10:3, b. Sanh. 110b -- Two rabbis discuss the question of whether the ten tribes will ever return to the land, as part of a discussion of Deut. 29:28. But this is about whether the tribes will, again, return to the land, not about whether they are lost.
Sifra 269.1 -- Here, a single rabbi applied Lev. 26:38 to the 10 tribes ("you shall perish among the nations"); but others took "perish" to simply refer to exile.
So it is that direct historical evidence speaks against the tribes being "lost" -- though some undoubtedly lost specific tribal identity as the ten tribes assimilated into local populations, and into each other. The only truly contrary evidence comes from interpretive sources and not historical ones.