I an in-game cutscene, Tyrande did say that we will one day return to Teldrassil when its roots heal and the Night Elves rebuild there. So perhaps we will see Teldrassil renewed again (and revamped in a future expansion).

Very cool. I hope this hints at the whereabouts of the Postmaster after Dalaran. Though, it's possible his entire post office was in a pocket dimension he made himself, and he's still safe. Spacey-wacey, timey-wimey stuff.