Il’gynoth’s statement: “From the earth, he draws strength. Our earth. Our strength.” seems to be a reference to the Faceless One known as the Black Emperor(because he takes on a twisted variant of Wrathion’s appearance).
That Faceless One is a master of the Earth just as Deathwing is. Of course it’s Ny’alotha’s Earth so it doesn’t mean he can control Azeroth’s Earth(at least not until Ny’alotha’s Earth merges with it).
“Five keys to open our way. Five torches to light our path.”
We now know that the Keys are Xal’atath Blade of the Black Empire, the Helm of Domination, the Heart of Azeroth, the Lantern of Helya and the Artifacts.
N’Zoth of course hoped that he would be leading the assault upon the Maw not us! He was as blind as Zul’s apprentice Vol’jamba. Zul said one must prepare for futures one has not seen.
Zul of course found out that he had fallen into the same trap as Vol’jamba did. The reason Zul was certain he’d survive was due to seeing Dazar ruling in his vision as well as his grand return. He did not realize the two events were unrelated and didn’t spare him from second death until it was too late.
Zul probably also saw Decay and Death everywhere which isn’t surprising since the Maw and Scourge will be attacking soon.
N’Zoth is just another Vol’jamba not some unimaginable horror we can’t comprehend.
Vol’jamba, Zul and N’Zoth aren’t the only ones of their kind: Yogg-Saron, Viz’aduum the Watcher, Velen, Elisande and Xe’ra all fall into the trap of assuming their sight is perfect only to be proven blatantly wrong!
The forces of Void, Arcane, Fel and Light all had their visions proven limited. Sargeras’s grand design came from Viz’aduum the Watcher’s visions of the future which led to his downfall.
N’Zoth’s visions do happen in some way or another but they lack context that helps him to win.
Murozond(who lived the terrible future) may have given N’Zoth some context enough to recognize that the Black Emperor was only a Faceless and that Sylvanas is allied with the Jailer yet not even N’Zoth is above Time anymore than Murozond was.
Murozond most certainly told N’Zoth of those who could turn the tide against the Jailer yet did not give enough context about N’Zoth dying to those Mortals no matter what he said or showed.