West? You mean South surely. I don't know about this whole Israelite Tribes bit either. The Jews of Alexandria made off pretty well and likely had a hand in merchant traffic heading south. You will find Celtic Mercenary graffiti there though.
So archaeological evidence as well as evidence through their faith show that the Jew's of Elephantine Island were practicing something different than that of the southern tribes. They were still in communication through what's been recovered to the Elephantine Papyri but what I'm saying is not so fanciful as it sounds.
Also yeah it's not west, when I was typing I was thinking (north) west of the Simien Mountains.
Elephantine just south into Sudan goes along the Blue Nile and the stronghold of Beta Israel was Lake Tana and the Simien Mountains.
Interestingly enough the origin story of the hebriac-pagan Agaw speak of traveling in the same direction as Beta Israel and the Weyto a hippopotamus hunting population also based around Lake Tana are also believed to have come from Egypt as well.
I know it sounds crazy but then again most people have no clue a second temple existed, especially one in Africa.