I once had a trio of sickly hens, rescued from an unhealthy situation. The first hen, a Production Red, died from hunger; shortly after that, her sister died. I was down to the last girl, who was perfectly healthy, and eating fine when she had her sisters. After those grils died, she stopped eating and drinking, and just seemed lost. Seh always made her light, high-pitched "where are you?" sound. Eventually, she died.
Chickens do miss their friends, and it will hurt them just as much as the humans that loved them...