Thanks to November 2017 patch for Cats and Dogs, dead sims who get culled will stay in the family tree and releasing them to netherworld will actually delete the sim.
Lately I have been creating ancestors for my sims, then having them die by different ways like old age (forced by cheat), fire, pufferfish etc. After all of their spirits have been released to netherworld, the family tree for my sims looks much nicer than one sim. I can see my sims' parents, grandparents, great-grandparents and other ancestors.
One of my latest "ancestor projects" include a sim, whose parents and father's parents all have died by over-excertion due to excersise while his mother's parents and cousin's husband's parents have died by old age. It can make interesting backstories, but it also seems like cheating to get more generations faster.
