That’s the back-in-time, alternate-universe Velen you’re thinking of that died, from Warlords of Draenor.
Main universe Velen is alive and well.
Nathanos’s soul will probably self-destruct when Sylvanas finds him and, despite his soul being in a desperate and lonely state that yearned to be reunited with her, her first words to him are, “Nathanos, we need to talk… I’ve met someone else.”
That story line wasn’t very popular. It may not get followed up in a main story kind of way. I suspect going forward Blizzard will take cues from more successful MMO models, as far as player retention. Making an MMO for lore hounds just doesn’t go anywhere. They don’t play the game systems in any meaningful way, they play the quest then come here to crap on Danuser for subjective choices. The lore should be ambiance, it should be mysterious, it should be misinterpretable. Writing these hard line novel style stories just makes people mad lol
The kind of lore that appeases everyone is EVE/Albion style. The lore is a basic framework for you to make your story within. People play those games year in and year out because there aren’t these hard walls built up around things to bounce off of.