It is already stated as an objective fact that the Old Gods do not die, nor live, they are outside the cycle.
It wouldn't surprise Me if they transcended even Time itself, effectively existing outside the normal flow of Time.
They can already perceive all futures, and Past N'Zoth was able to perceive the past, present, and future of the Player character.
The Old Gods are special, the Old Gods are unique, the Old Gods exist outside the cycle.
Of course, their decision to manipulate and corrupt Nozdormu and his dragons was genius and also boosts their control of Time. The corruption of the Keepers of Time allowed them to gain an entire faction that manipulates and controls time, giving them the ability to disrupt the timelines to their advantage.
This is effectively what the Old Gods have been doing since TBC. They had their minions, Murozond and the Infinite Dragonflight, disrupt the time-flows, by preventing the rise of future enemies like the Horde and the Scourge (preventing the orcs from crossing into Azeroth; preventing Thrall from escaping to Kalimdor; preventing Arthas from completing his destiny in Northrend; all done to create a timeline where the Old Gods' enemies are removed from existence).
The Old Gods, with their Infinite Dragon puppets, have the ability to disrupt Time and we shouldn't underestimate this power that they have.