I think I read/heard from Rav Avigdor Miller that there’s a guarantee that no Shevet will ever go out of existence.
The Gemara says (Megillah 14B) that Yirmiya haNavi brought back the Shevatim before the destruction of the First Bais haMikdash (not necessarily all the members of each Shevet).
The story of the Baal Akdamos crossing the Sambatyon is apparently a legend – according to the story he could not return,
that not being pikuach nefesh, but he is known to be buried… I forgot where. A known location. So says Hamodia Magazine.