I'd call it "possible", if in addition to restoring the provinces and gems the
PCs were close and friendly with Tuarhievel and the Sielwode, had helped both
nations expand their forests, had destroyed Rhoubhe, and were directly
responsible for saving Lluabraight from going under to the Gorgon, White
Witch, and/or Urga-Zai.
And that's if an elven regent is numbered among them. Lluabraight is almost
as hostile as Rhoubhe.