If i guess this correctly, you want to assume that Old Gods basically "live on" without body, like some spirit survives or lives on?
Maybe we should ask ourselves whether that has actually any ground to stand on in the first place.
Y'shaarj:
https://wow.gamepedia.com/The_Last_Gasp_of_Y%27Shaarj
Basically: The last remains of Y'shaarj are a dark smear on the Floor and anything related to Y'shaarj (like the Sha) will also fade to exist.
C'thun:
https://wow.gamepedia.com/C%27Thun%27s_Legacy
Furthermore, Cho'gall tried to ressurect C'thun, you gotta be dead to get ressurected.
Yogg:
Yogg himself calls his own body a corpse, so yeah, he's dead.
The fact that he also states said corpse "will choke this land for all eternity" gives you a hint that Northrend might face a similiar fate as Pandaria on the long run.
Just to put that out from Afrasiabi from a Blizzcon 2018 interview (source is in russian on WoWpedia, so i can't check it):
Basically, for now, they're dead and remain that way unless something changes.