I don't know what you think about it, but I think burials should be somehow represented in the game. I saw somewhere that you wrote that originally you had no plans for citizens to die of old age but now you're thinking about giving them long life. I like the idea of citizens dying of old age because it's simply realistic. And when they die - they should be buried somehow.
But I'm not thinking about need of building new grave for every dead citizen because it could make game too complicated and with too much micromanagement. It may be done however in a bit different way:
At the beginning you could choose the way your tribe bury their dead - throwing for animals to eat, burning or burying in the ground (some cultures may have only one historic option - like burying mandatory for Egyptians). Then, during game, players would have to mark a part of land for cemetery - nothing else could be built there and, as game progresses, new graves would be automatically added, just to signify the progress and that burials are taking place there, but without the need to micromanage all these burials. When player run out of space there - a new patch of land should be marked as cemetery.
Now - throwing bodies for animals to eat would require least space - just a patch of land or small tower (like in Persia) where bodies would be dumped (building or patch of land could change with time to show more bones lying there).
Burning would require more land because there should be place for the funeral pyres (burning from time to time to give impression there's funeral there) and small graves where jars with ashes were buried.
And traditional cemetery with traditional graves where whole bodies were buried. This cemetery would require bigger space than other ones (actually not "bigger space" but there would fit less graves there than on the burning one because graves would require more space and therefore less of them would fit the same space).
There could also be cemetery looking like small caves where jars with bones could be deposited.
That's what I'm thinking about (forgive crudeness, I'm not an artist ;) ) - in this case it's a burning grounds with small graves containing pots of bones and ashes:
Of course some cultures back then were burying their dead inside their homes (under floor), but forcing players to care for the dead and designing some space for cemetery would give better immersion (and improve health and happiness when we think about in-game benefits).
These would be graves for common people. Pyramids/mastabas and other monumental graves should work like monuments IMO.