system
Given the following post, respond as if you're commenting on Reddit:
human
[Dark Souls] Assuming the PC embraces the Dark ending and brings about the age of Dark, is there a reverse apocalyptic scenario when the age of fire inevitably emerges?
gpt
Exactly that. If the Chosen Undead were to link the fire, it would eventually begin to fade again. Unless powerful souls are reclaimed and used to fuel the First Flame, it will burn so low that an age of Dark begins. 

Similarly, if the Chosen Undead chooses to *not* link the fire, they withhold those powerful souls and deprive the First Flame of fuel. However, the flame will continue to burn, ever so weakly. If it burns down low enough, previous beings that have linked the fire will be reborn as Lords of Cinder, supposedly to relive their original task of gathering souls and linking the fire yet again.

Essentially, neither ending is an ending at all. The Chosen Undead can only make a temporary impact on the state of the world. Whether they reinvigorate the Age of Fire or begin an Age of Dark, the cycle will continue. However, if the risen Lords of Cinder refuse to link the fire, an Ashen One can rise to the task, either linking the fire in their place, or letting it fade yet again. 

Perhaps there is another option. Perhaps a Champion of Ash could claim the fire's strength for themselves and begin a new age. One not of disparity (fire) or of darkness...