If you won the Battle of Yenwood, I believe the Ambassador notes that Caed Nua is yours will be your descendants', so you're not merely a viceroy, but the actual lord of Caed Nua.
I'm not an expert, but I'm pretty sure if your land is destroyed you can still have your title if you are landless. There were plenty of disposed kings or emperors in history that went into exile wearing their empty titles, I'm pretty sure. But the Watcher still has a better case then them, he probably still owns the actual land.