Alright, so along time ago, I bought sims 2 and pets. (I had to rebuy it cause my computer crashed ) I had a family- One dad One Mom One child. Then one day as I was playing the lot to my demise, I clicked on that sim (his portrait was gone) and I couldn't find the plumb-bob anywhere. I played a while later and his box without a portrait disappeared. I searched the entire lot to see if there was a grave or urn, but nothing. When I was checking the memories to see if he got abducted, I noticed something odd. All of the memories of him was changed into Mystery sim, and the made out one was changed to "Made out with (simoleon sign)Subject" No portrait. I didn't know if he was choking, as I couldn't find him anywhere. I checked the relationship panel and he was completely deleted from the family tree! I checked the Sims Wiki (wikia) at death and found the mysterious choking death, which was caused by an error in the disease coding. He didn't get a disease anyway. Because the death itself sounds glitchy I made a scenario: Somehow the error triggered causing his portrait to turn blank and making him unselectable, and so the error deleted him permanently, and so no grim reaper or no death memories plus no tombstone/urn. I also found out that in the Capp family most of the people's memories is "(Simoleon)Subject died" Any answers would be appreciated.
Also, I wasn't using cheats,hacks, mods, or CC at the time.

It is far more likely that your neighborhood data became corrupted. Is there any chance you moved occupied lots into the lot bin or deleted Sims from the neighborhood Sim Bin? Those would be the most common causes of neighborhood data corruption.

I don't think so, all I really remember was that that happened, and that somehow out of the sky, my create-a-sim sims kept running in and shoving sims (I got really angry) so I moved them out so yeah I guess that could be it, but that was in strangetown... ^ I know one of my current neighborhoods is corrupt because I can't have babies without the game crashing, and I put to far much effort into creating it so yeah.

This actually happened to me once, But i didnt think anything of it as i nevered played the family it happened in much anyway.