Killing an active Sim?? Still need help, please.

I think Clement has a hidden trait that makes him immortal like Baby Ariel has. I'm not sure if you can kill him off without cheats/mods.

I had a sim have a child with him, and I was originally planning to let him live in the family graveyard whenever he passed but he's just not dying. I'm thinking about just moving him in with Vlad at this point.