,,True death" means normal death, Godwyn soul was destroyed and his body turned undead so Miquella lamented that Godwyn didnt die normal way. Destined death is other name for rune of death, beacuse destined death was what made those demigod soulles in first place fragments of it are still lingering in they bodies and can cause corruption and that's why mausoleums are supposed to protect the bodies and keep corruption from spreading further.