It's a bit of a reincarnation scheme; the souls get cycled through, ideally, the Nasan falls, which flows through Miphas and Sharzunates. Reward and damnation are not supposed to be eternal in these schemes, but time served.

That being said, Aroesus started to play with that in order to hold souls (power) in reserve for his own purposes and other deities may well seek to do the same. 

So the punishment and reward isn't so much an eternal thing as time served before you get put back into circulation again. If allowed to run its course naturally, anyway.