Good use of sources, haven't seen that in a while. edit: And a fast writer too.
While Frontier, Conquest, and Accommodation doesn't exclude the possibility that came to Tamriel from Atmora, their presence all over Tamriel and Yokuda does suggest against it. At least without further information on when and how they spread, they should be assumed to have been there ever since the end of the Dawn.
But lets get to something more fundamental. How do you lose an entire continent while you're on it?
The conflict itself is elaborated in the Anuad, it's also referenced in Faith in the Empire and the Monomyth.
A large fragment of the Ehlnofey world landed on Nirn relatively intact, and the Ehlnofey living there were the ancestors of the Mer. These Ehlnofey fortified their borders from the chaos outside, hid their pocket of calm, and attempted to live on as before. Other Ehlnofey arrived on Nirn scattered amid the confused jumble of the shattered worlds, wandering and finding each other over the years. Eventually, the wandering Ehlnofey found the hidden land of Old Ehlnofey, and were amazed and joyful to find their kin living amid the splendor of ages past. The wandering Ehlnofey expected to be welcomed into the peaceful realm, but the Old Ehlnofey looked on them as degenerates, fallen from their former glory. For whatever reason, war broke out, and raged across the whole of Nirn. The Old Ehlnofey retained their ancient power and knowledge, but the Wanderers were more numerous, and toughened by their long struggle to survive on Nirn. This war reshaped the face of Nirn, sinking much of the land beneath new oceans, and leaving the lands as we know them (Tamriel, Akavir, Atmora, and Yokuda). The Old Ehlnofey realm, although ruined, became Tamriel. The remnants of the Wanderers were left divided on the other 3 continents. - The Anuad
Now what is described as merely ruin, should be taken in the context of a war between et'Ada. For a better impression I'd have trace down a text that describes the submission of Summerset by the Numidium while it sings world refusals, and that was only one god.
However, even though Old Elnofey, that is Aldmeris, became Tamriel, according to timeline, the Altmer weren't on it.
The Aldmer began to split along cultural lines, on how best to spread creation and their parts in it. Each Tower that was built exemplified a separate accordance.
This sundering of purpose is the myth of the "destruction of Aldmeris." Outside of the Dawn, and even then only in the dreamtime of its landscape, there was never a terrestrial homeland of the Elves. "Old Ehlnofey" is a magical ideal of mixed memories of the Dawn.
Do not believe the written histories.
All mortal life started on the starry heart of Dawn's beauty, Tamriel. - Intercept
The intercept follows the same line of thought, Aldmeris only existed in the deep end of the Dawn Era. However unlike the Anuad, Nu-Hatta considers Tamriel to be the birth place of all mortal life.
While this should settle what happened to Aldmeris, simultaneously a concept, an ideal, a place in a period where gods controls the events in time as if it were a war. A period in which early Aldmer tried to retain the extreme organisation and order of Aetherius. There is no real resolve on who was where when.
This is a fundamental problem of the border of the Dawn and the Merethic, when the et'Ada gave up their hold of time, by leaving or surrendering to Mundus, the individual timelines they created would be put together. While the people would still retain memories of the Dawn and it would seem as if there was no real change, but to us and other people used to a synchronized time it would be as if everything appeared at once. Literally as if one were to start a new a new game, anything prior to it would merely be a story.
A story that in this case is more then seven-thousands years old and rife with ideology, but I'll leave those anolysis to others.
edit:
Some more about what the war in the Dawn Era would look like.
http://www.gamesas.com/bgsforums/index.php?showtopic=921446&st=80#