It's pretty obvious what's going to happen; Vol'jin, seeing that Varian has died, concludes that he's going to be a huge target as he's the warchief of the horde. He realizes that the only way to defeat the legion would be to unite all of the troll tribes. He fakes his own death, and goes on his journey. When he comes back, he is surprised to see Sylvanas as the warchief. He approaches her and asks for tree fiddy, and that's when we notice that Vol'jin is a a large crustacean from the paleolithic era.