One little footnote to my squashed chick -- I hope people don't find this gross or upsetting.
When I was sure it was dead, I put it back on the ground near Momma hen, so she could see that it was dead. I was worried that she would be frantically looking around the yard for it.
She starting to peck it gently, and I was getting teary. Then, when it was clear it wasn't moving, she began to really tear into it and I realized she was going to try to eat it. At that point I took it away. I forget, sometimes, how practical chickens are.
She and survivors are all acting pretty normal now. I hope they have short memories. I wish I did.