The cats in throughout my life passed on for different reasons:

Paddy had leukemia and died when he was a few years old. This was before the vaccine was available.

His his mother Cricket, his sister CC, and CC's daughter Cocoa all lived long, happy lives (18+ years) before passing naturally.

Katie died from kidney failure after a short illness.

Samantha got lost outside and never returned. She was only 2, and I have many regrets about her disappearance.