I figured that anyone in a Death Cult would want to somehow immortalise their sacrifices, so why not eat them.
A solid reasoning that has historical ties
Would that be Maya and Aztecs again you mean? the alleged cannibalism of The Maya and Aztecs has been subject to much debate. No conclusion seems likely in the foreseeable future.
Among tribes who really WHERE cannibals beyond a shadow of a doubt I don't think they specifically where followers of death cults.
Two types of cannibalism typically prevail:
1. The ancestorcult variety. In this you eat your dead relatives in order to preserve them - body and all - within the clan/family. Distasteful maybe but not very aggresive. Unfortunately it has lead to a disease called "Kuru" which essentially is a disease that strikes as brainfever. It's the same as "Mad cows disease really" and has the same causes (grinding down cows bones in the pellets for the cows is one of the reasons for Mad cows disease) so it seems to be a disease caused by eating something that is TO genetically close to the eater.
2. The "Sympathetic magic" variety where it is believed that eating, for instance the heart of a strong warrior, would let the eater gain some of the strength of that strong warrior. This type of cannibalism is more common among warlike aggresive tribes such as for instance the Marind Anim of Iryan Jaya/New Guinea.
I doubt there even is any real HISTORICAL precedence of death cults. That's more of a fantasy thing. The closest thing to a death cult would be the "Left hand" tantric followers of Shiva/Kali such as the Kapalikas (skulleaters) among the shiva worshippers and the Thugees among the Kali worshippers.
Kapalikas live in graveyards, use human skulls as food bowls, paint themselves in excrements and so forth because left hand tantrism operates from the belief that one way of showing that the material world is an illusion is through really entrenching oneself in the most vile and disgusting habits. For the same reason there HAVE been Tibetan buddhists who actively engaged in sexual orgies and the like.
(This is opposed to RIGHT handed tantrism that means that since the world is an illusion one should strive to live a pure and ascetic life in order to show ones disdain for it.)
For much the same reason the Thugees used narcotics and strangled travellers.
But none of them really worship DEATH as such.
The british of course claimed the Thugees to be a "death cult" and swiftly rooted them out.
