pretty much this.
The novels are often meant to show events happening before it happens ingame, like the shattering, twilight of the aspects and tides of war.
Odds are, vol'jin will be doing some not shown ingame yet, off camera if you will, and we catch up with him in a following patch.
If everythings right, it will go Thunder King Raid - Following patch will be new quests and story content - Following patch the final raid of orgrimmar.