*edit* You can still get the quest! You go to the Windrunner Spire..I think in the Ghostlands. Kill them till The Lady's Necklace drops. Thats the quest. After you take it to Sylvanas she sings the song. And you get a book of the lyrics. In both languages they are..
English..
"By the Light of the sun.
Children of the Blood.
Our enemy's are breaking through
Children of the Blood.
By the light.
Failing Children of the Blood
O Children of the Blood
By the Light of the Sun
Failing Chrildren of the Blood
They are Breaking through
O Chrildren of The Blood
By the Light of the Sun
The sun."
Thalassian.
"Anar'Alath, Anar'Alath belore
Sin'Dorei.
Shindu Fallen Na
Sin'Dorei.
Anar'Alath
Shindu Sin'Dorei
Shindu Fallen Na
Sin'Dorei
Anar'Alath Belore
Shindu Sin'Dori
Shindu Fallen Na
Sin'Dorei
Anar'alath Belore.
Belore"
Sylvanas use to sing this song (in WoW) after a quest..I don't know which quest though and I think they took it out. But its the Blood elve Eversong Woods background with her singing