Trolls have a bad habit of not staying dead, at least not entirely. Troll ghosts are very common, and there was that one from Pandaria who flat out resurrected himself. But with the demon poison/curse that killed him supposedly effecting his soul...I'm not sure. He might be gone for good, but there is a good chance the voodoo ghost of Vol'Jin will show up to spout some FO DA HORDE every now and again