Tyrande underwent the ritual of the Night Warrior and launched a counter attack on the Darkshore, aided by the Gilneans (see the story and warfront in BfA)
They took back most (but not all) of the Darkshore, yet what they took back was plagued, destroyed and haunted, thus uninhabitable (see the book "Exploring Kalimdor"). They thus took Hyjal as their new home and kicked out all members of the Horde who resided there (see the book "Shadows Rising")
When the Horde and Alliance signed a truce, many Night Elves")
In Shadowlands, we learned that the souls of all the victims of the Fourth War (including all the Night Elves) were sent to the Maw, where they were tortured and turned into abominations.
As part of the Night Fae campaign, many souls from Teldrassil were rescued from the Maw and brought to Ardenweald. There, they sacrificed themselves to create the seed for a new world tree.
Since then, the seed has been planted and nurtured in the Emerald Dream. In the upcoming patch, the protodragon Fyrakk and his forced attack the new world tree and try to claim it for themselves. The next raid tier will be all about defending the new world tree, and the Night Elves are already leaving Stormwind to move to the new tree which is growing on the Dragon Isles.
Meanwhile, Sylvanas is doing her penance in the Maw, trying to save the souls that can still be saved.
The recent Night Elf heritage questline shows that the Night Elves are becoming more open to change, which includes that men are now allowed to have facial markings.
The Kaldorei Dark Rangers are now a customization option for Night Elves. We're told that "they are allowed to return to the Alliance if they wish to do so" but all known NPCs continue to stay with the Horde
