The mythological stories of the death of the sun king/hero/god (such as the story of Llew in the fourth branch of the Mabinogion) have often been taken to mean the death of the sun at the summer solstice and rebirth at winter solstice, and may have been misinterpreted to mean a need for actual human blood sacrifice by some.
I believe that the ancient tales mirrors and the experiences of some of the ancient bards, who, in common with some of the inspired poets and mystics of history, experienced what is known as "The Dark Night of the Soul".
The death of the sun king refers to this experience, which is a psychic sacrifice or death, an ordeal that one must get through before you can experience divine inspiration (or rebirth) once again.
This psychic death experience is not mere depression, but a trickster (or Loki/wolf) experience --- it can begin in a manner similar to the good connected (Odinic) highs but rapidly turns sour. The bard loses his connection with the natural world and it in fact begins to turn against him in the form of paranoid delusions and distortion of sensory input. It the experience there is the racing mind of mania but the emotional loss of depression. This is known as a mixed episode or a type of dysphoric mania, and is more dangerous than the classic euphoric/poetic mania.
In the story of Llew they mention a period of 180 days (or 180 tempests) which is closer to a full moon to full moon separation, so maybe "6th new moon after the death" got translated to "6th full moon after the death", or 6th moon was taken to mean 6 full months instead of the 6th appearance of a new moon.
Traditions which say they tore a sacred king to pieces (or actually did), or of a sacred king or avatar or god/goddess coming to pieces (perhaps figuratively, as in coming to pieces meaning mental problems), I believe are based on the distribution of the words and ideas of the inspired mystic to many fields during and after his/her episode. Hence some in the past at least may have provided Renaissance type clues to many fields of endeavor as well as religion. The pieces of the sacred king represent these many inspired clues. The death of the sacred king could be his/her passage from inspired back to normal or delusional at/after new moon; back to ordinary status, while the essence of the sacred king, the clues, are passed around. (Or the death could mean a waxing gibbous moon trial period with release at full moon, or a descent into the low years for seven years.) This again shows the temporary nature of the divinely inspired period and how much one has to pay to reach this state. So people in early Christianity who held on to the old blood stuff to gather adherents from bloody cults made a mistake, they could have explained it like this.