印象里不朽者貌似和凡人信仰没啥关系，它们受到的约束主要是自己所属的界域以及大佬们定下的不能直接干涉凡人的条例，死亡条件也是在自己所属的homeplane被杀，没有提到信仰的事。
不过这本我也只是粗略瞥过，可能看漏了，最好让对方给个原文具体页码和段落啥的，这样也好对照一下。

在《不朽者之怒》第83页。
Fading
The link between Immortals and their followers is not well understood, even by the most knowledgeable Hierarchs, but all Immortals are aware that without a following, they can slowly fade away to nothingness.
This sort of thing happens very rarely, but it can occur when an Immortal has seen his or her followers abandon their faith after to a number of destructive Strokes, if the Immortal victim is then imprisoned and unable to recruit more followers. It can also happen if an Immortal goes to another dimension and disappears completely, only returning to the multiverse after all his or her followers have long since died of old age.
This fading begins a full year after the Immortal's last mortal follower dies or abandons his or her faith. It takes ten years for the Immortal to fade to nothingness.
However, an Immortal who has faded to nothingness is not dead; he or she still exists as a dim and undetectable life force on his or her Home Plane and can be revived if the conditions are right. If later- day mortals discover ancient writings about this Immortal and decide to follow his or her teachings and devote themselves to his or her philosophies, he or she will hear their call and awaken. The newly-revived Immortal will once again be a 1st level Initiate, but he or she will be Immortal again.
Initiate Immortals who serve the higher- level Immortals who acted as their sponsors share the benefits of their sponsor's followers until such time as they end their service. Independent newly-Immortal Initiates tend to be very busy in their first decade creating a mortal following.