Though the codex also goes a long way towards explaining that the Necrons did lose their souls when they gave up their mortal existence, and Necron Warriors are pretty much still the soulless automatons they used to be (and the fate they suffered is, in a certain way, presented even more terrifyingly in the new codex, as it focuses a lot more on how much the Necrons lost by their transformation, and how for the vast majority of the population, this change was anything but voluntary). It also explains how this change is, without exception, slowly causing them to go insane, in varying ways: Destroyers adopt a nihilistic philosophy that calls for the utter extinction of all life, Lords become increasingly disconnected with reality in various manners, Flayed Ones... Flayed Ones are just utterly messed up beyond repair.