There are rumored to be small clans of "true" Akaviri still on Tamriel, though the details are sketchy. At this point, the Tsaesci and Akavir in general disappear from historical record, until the time of Uriel V and his Akaviri invasion.
It was not until Reman Cyrodiil, in 2703, when the Akaviri invaded Tamriel, that the whole of Cyrodiil united against the attackers. By the end of this war, which culminated in the defeat of the Akaviri invasion force in the Battle of Pale Pass, on the Skyrim border.
Undead Akaviri Soldiers were men who lived long ago but were then extinct by Tsaesci.