With the help of the Shadowmasters, we can summon back the spirits of the fallen. But it is a mixed blessing. The body the spirit inhabits is made of energy and is easily dispersed. It also cannot interact with the physical world much.
Only strong spirits can be summoned back. A fighter needs to have a VooDoo Power of 40, Bravery of 60 and Reactions of 60 to be able to return in this fashion. Crossing the river Styx has its price, though: 10% of experience gained on all skills except VPWR and BRA will dissolve into nothingness. No Augmentations carry over, either.