I didn't say (or didn't mean to say, at least) that the culture of your del-korm was anything less than credible, I only meant to say that the culture itself not necessarily made them incompatible with the Prophecy afterlife. As I also explained they, due to their culture, would not harness as much... let's call it "bad karma" for doing the things their culture permits as others would, and it would be much easier for them to counteract this with deeds that earned them "good karma"; it would still be a bit of an uphill struggle for them to be prominently good and earn access to the Upper Plane, but this would only support the need for them to do as much during their lives as they could, basically to gain enough reverence from themselves and their own kind to balance out the innate revilement of the other civilizations.
Not that any of this matters if you're determined for them not to have an afterlife, I was just trying to bring the point across that it was possible to work out a compromise on their side rather than ditching the concept of eternal souls.

What creatures do not have afterlives... Well, one of two criteria has to be met for a being not to have an afterlife. The first is the most easily achievable one and was included in the very first question I asked when I learned that the del-korm would not have afterlives: faith. If a mortal firmly believes that they will not have an afterlife but has an idea of what will happen with them instead, then their own conviction will cancel the Wanderer's duty to bring them to the traditional afterlife and instead enforce the fate they believe they will meet. In other words, if the del-korm take this route they not only need to have no doubts that they will not have afterlives (they need to [I]know[/I] it), they also need to be confident in what will happen to them instead.
The other criteria is simple and is the most common reason to beings not being entitled to an afterlife in the first place: they are not mortal. Only mortals have afterlives. Now, "mortal" in the Prophecy refers to beings that meet their own set of particular criteria, and failure to meet even one of these will land them in a different category of existence. One: they have both of the Seeds of Good and Evil; lacking either will drastically affect their psychological composition and leave them with an innate desire to satisfy the Seed they have, or no desire to do anything at all if they have neither. Two: they have independent souls composed of mortal energy, drawn from other mortals, ambient energy in Reniam and/or from the Spirit Realm during their sleep. Three: they must be bound to a living physical body, which excludes beings like ghosts and true undead (vampires, contrary to popular belief, are not counted as undead in the Prophecy, but are considered mortal)... and I think that's about it. Straying from any of those three criteria will make a being unfit for an afterlife and will render it a different existence altogether.