Are they dead or just dormant?
I believe the canon answer is that we beat them so badly that it’ll take them millenia to recover, but they aren’t fully dead. It’s nearly impossible to truly kill an Old God, as evidenced by Y’shaarj, who despite being ripped out of Azeroth and crushed by a Titan, still has influence and effectively cursed the entire continent of Pandaria.
Hmm, apparently you can’t link stuff from the old forums here 
But there was a similar thread back in 2017 where a blue post confirmed that Old Gods cannot die, the quote reads
They do not die, they do not live. They are outside the cycle.
Which would indicate that even Y’shaarj isn’t truly dead 
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Y’shaarj is the only one confirmed Dead, Aman’Thul ripped him out like a bad weed…
They’re kissing in a tree.
I think they were quoting Herald Volazj who says that in Ahn’kahet.
It was confirmed that C’Thun was killed but his remnants (Like what happened with Y’Shaarj) & dark soul still remains around the vicinity. That or he feigned death and has merely been biding time, but who knows.
Yogg’Saron was extremely powerful, (So much so the Titan Keepers built their fortress around him, to help keep contained) and managed to poke his head out of his prison - which we went whackamole on & pushed him back in. But he’s still very active, alive and kicking. In Legion Questlines you see servants of the Black Empire infiltrate Ulduar in attempt to help rise again. Yogg Saron was only able to poke head out because Cho’Gal weakened (Not broke) the bonds, the seals and bonds that held Yogg’Saron were described as too powerful, so he merely did what he could with given ability. As is described in the Chronicles book series.
N’Zoth is the only largely active one that is without constant monitoring / free to do as pleased on Azeroth.
Cthulhu’s pet, Dog Sothoth…
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