I'd be interested to see what
@Shadrach has to say. He is more familiar with smaller flocks than I am.
Chickens are prey animals that flock together. As they evolved they developed an ability to move on when one was lost, otherwise the entire flock would be at risk. Losing one, especially one higher in the pecking order, can affect the entire flock but usually not for long. They tend to get over it quickly. It is a survival mechanism. If a broody hen loses one or more of her chicks she keeps taking care of the others. She may look for a lost one or cluck to try to attract it but she tends to not obsess over it. She does not want to lose the others. And if she loses them all she is usually over it in a day or two.
However they can form bonds. Each chicken has its individual personality. I often see cliques within the flock where two or three form their own sub-group and hang together within the flock. And may even leave the flock for short trips together.
From what I've seen there is very little grieving as we would describe it but you can have a few that appear affected for a day or two.