A similar thing happened to me a few days ago. I noticed a 78-year old master scientist hobbling around slowly so I decided to pension her off as a doctor, and let her spend the rest of her life doddering around in peace. I switched her preference in the details screen and picked her up to take her to the cactus so she could gain a little knowledge of medicine. She disappeared and her bones suddenly appeared in the middle of the village. I can't help thinking the shock of being picked up was too much for her, or perhaps it was the sudden career change ...