I think those lost in the void died quickly, either from being ripped apart by ghost leviathans or being crushed by high pressure. These fates are marked by short, sharp moments or fear or horror, but I don't think the are really sad. Keen from pod 19 had a pretty tragic end- trying so hard to save the survivors, only for his efforts to end in failure and inevitable death, but I'd say the saddest is Danby's story from pod 12. He ended up alone in a pod, trapped too deep for even a die-trying chance to escape, forced to watch his death gradually draw nearer with advanced kharaa infection. The only meaningful thing he was able to do with his final moments was confess his dishonesty to a tape recorder, like some miserable attempt at a deathbed redemption. A pathetic, hopeless and lonely death.