I think that Varian and Vol'jin are alive.
First, at Varian funeral, there is no body displayed, just the coffin. I immagine royal funeral to be kind of like what they showed on Game of thrones. There is body displayed for mourners and then they put it inside coffin and into tomb. This is not the case of Varian. There is just the stone coffin. Also there is no real Shalamayne on it, just some carving. The fact that warriors doesn't get weapon from one of the most powerfull warriors of his age that is also kind of a magicall, instead some random viking swords could mean, that Shalamayne could be still with Varian.
My hypotesis is, that in the broken shore cinematic, when Gul'dan summons all the demons, Varian quickly orders to retreat, while charging the army of demons. The last thing we see, is Varian slaughtering hordes of demons (kind of Ga'nar type/Broxingar cinematic) and then, Gul'dan uses his fel magic to lift him up (like hi did to Tirion) and throw him into the portal (like he did with Grommash) with his sword. Players and Grenn assume, Varian is dead and makes him a funeral, but only the statue on coffin is displayed, because there is no body.
On the horde side, there could be something similar but with Vol'jin.
We will end up mourning Varian and Vol'jin just to late find, they were sent trough the portal (maybe to Argus)
I like this idea!