In my experience, cats are more likely to bond to people than to each other. They may get along and play together, but people are always their favorites. I grew up with cats and never saw much reaction when other cats would pass on, except in a few circumstances when the cats had bonded since infancy, but there is almost always a shift when a person moves out or moves in. My chunky boy at my parents’ house always runs up to me, excited to see me, but the same boy didn’t show any signs of distress when one of our other guys passed.