The Brithini have immortality because they haven’t changed since Death appeared. Here’s a Brithini story I heard:
Why we live forever?
When Zzabur asked his father, “How do we stay immortal?”the Prophet answered simply. He said, “Do not change. Do what you have done. Act within the Laws and Ways you have been given, for they are immortal. Your actions embody the One, your bodies enact the One. Anything new from this moment forward is Death.”
Thus we were never severed from Life, like the rest; from Magic, like the rest; from Divinity, like the rest; from Good, like the rest; from ourselves, like the rest. We are not mortal people, or gods, or good people, or our own people — we simply are. All else is a wane shadow of us.
When we die, the world dies. We are the last holders of the One. When we are gone, all else will go to. When we are gone, everything left is corruption and death.
It is not possible for those not already Brithini to become Brithini.
And so although the Rokari are very much an attempt to return to pre-Hrestol Malkionism, they are post-Brithini.
Even having a child would be change? unless it was done exactly like it had been done before.
Would it be possible to become a brithini through heroquesting? Heroquesting is not a mere magic wand. Perhaps if we lived a life that was EXACTLY like it was before Death, and refused Death just as the immortals had, we might be accepted as pre-Death by the immortals. But how do we get there, when the very quest itself is outside of the pre-Death experience? More likely we would end up with a different result than anticipated (this sounds more like a Gautama quest – we will discover and accept Death rather than refuse it).
I tend to think the Brithini are in a closed system.
Does this closed system work in the Brithini’s favor come life-threatening instances such as combat. Death is not aware of them. They are pre-Death and maintain all appearances as such? If they are forced to embrace Death, they will die. Hit them with a sword, and they die – as that forces them to change.