I'm not exactly sure how this invalidates the quoted post and why the "or" was needed? Regardless of what happened to Varian's soul, his death was represented (besides the obvious explosion) by the light of his sword extinguishing, fading into nothingness as his soul moves on to whatever its destination might be. Doesn't matter if it was into the light, the Emerald Dream with Goldrinn, or even the shadowlands or Gul'dan's last bag slot where he keeps all his filled soul shards stored. The point is, he died and the director/or writers decided to symbolize that through his weapon.
Not sure if you've noticed (likely not since you are even trying to make that point) but the characters in the game have grown slightly beyond the scope of basic Dungeons and Dragons necromancy.. and by slightly I mean massively... and by massively I mean the standard "rules" don't apply
Varian will be back by the end of the expansion.
If WoW was a DND setting all Paladins players in the game would be Fallen Paladins.
FACT
you need to also beleive in valajar (wows valhalla) to go there, why we only see vrykul because they beleive in it, and we see it first hand infront of us during the warrior artifact quest, so we beleive, and when we die, we go there because we beleive, and the other players are those (other people who come to beleive in it) thing... so no he is not
The real question is did we actually see him die? I mean all we saw was an explosion of fel energy and I could totally see blizz keeping him a secret end raid boss that was "turned" by said fel energy and not actually killed.
It is completely possible, technically.
Sylvanas is an example.
She was murdered and raised as a spirit (=no body required).
She killed herself by using saronite that could "destroy" her body and soul.
She was brought back from that state by Valkyrs, from the "other side".
So it won't be "bending rules" at all if Varian comes back. However, the way he went... I kinda doubt he will. I think, like Arthas, his story is at an end.
I think Gul'dan destroyed his soul. He's gone for good, erased from existence.
It's safe to assume the explosion was him, but we know nothing about his "soul being destroyed". It's purely speculation.