What lore do you ignore?

[Iscah]

In the case of G'Raha (Crystal Exarch) in particular, he did not cease to exist upon averting the 8th Umbral Calamity, which suggests his actions did not remove/overwrite the conditions required for him to exist, which is proof his original time stream is still intact and running parallel to our own, where our own time stream is diverged from his original time stream.

I know that, but that would be indirect proof – we can logically reason that because G'raha still exists, the timeline he came from is likely to still exist.

I specifically wrote "direct proof" to mean confirmable evidence that the timeline exists: some way to look across the high-degree dimensional split and actually observe the existence of the other timeline. To our knowledge we have no device that could do so and assure G'raha that his friends' reality continues.

On a pedantic sidenote, "G'raha" (as for all Seeker names) doesn't have a capital on the start of the given name when the tribe letter is used. I assume it might be a limitation of forcing player names to start with a capital and then lower case for the rest.