ok building on the idea of a reincarnation system, and what seems to fit the lizardmen..
so when you die, you go to the
Abode of the Old Ones (which if asked where that is, skinks will tell you "the otherside of the stars". saurus and slann will ignore you) where your spirit is refreshed and can give them your memories of your small part of the Great Plan, before they send your spirit back to be reborn in a new spawning. however since you gave them your memories, you do not remember your previous life, though previous spawning s might recognize the spirit within you through various personality traits shared with previous lives. As there are far fewer spawnings and cities now than there once were in ages past, it is believed that some spirits are kept with the Old Ones until the time is right for them to return, and it is these ancient spirits that become the great heroes, as part of the Great Plan.
Since Slann do not spawn however, their spirits are believed to stay within the geomantic web, but without a bodily vessel to inhabit their memories will be gradually lost completely. thus the Slann are mummified and entombed within the temples, so that their knowledge will be preserved until the day the Old Ones return to the world.
as far as death rites go, i could see Saurus, Skinks, and kroxigors being given a brief period of lying in state, before being left for
Excarnation, that is, left out for animals and bugs and such to consume the flesh. odds are that the cities would have dedicated sites in the jungle for this, with something akin to the
Dahkma of the Zoroastrians, where the bodies can be placed for animals to reach them but still watched. odds are that insects would deflesh the bodies quite rapidly even before large animals would get to them. on campaign i suspect they'd do like the Plains Nations of North America did in older times and
place the dead on scaffolds or in trees. Which would amount to much the same thing functionally. i do not think they would retain the bones of their own kind, so i suspect they would only watch the sites to ensure that no one disturbs the bodies before they are consumed by nature (preventing large carnivores from getting to them, or necromancers raising them as zombies, etc) but otherwise would not intervene.
Tying into the Slann thing above, you could easily have it that they believe that the spirit remains tied to the body, and for the spirit to go to the old ones the body must be no more. thus the excarnation. they have to ensure that the body is gone so that the dead can fulfill their cycle of life and rebirth.
