I had a chick stepped on pretty firmly by a 70 lb black lab mutt. She was dazed and wobbly for about a day, maybe two, and closed her eyes and stood there and wobbled a lot. I thought for sure she was a goner. But she still seemed interested in eating and drinking some, and perked back up after a couple days. Now she is the biggest of the three and doesn't seem a bit the worse for wear.
Each of the other two chicks were stepped on in the first week or two, despite what I thought we pretty good precautions, by a 2 year old and a 4 year old respectively, though not that badly. They were over it immediately. So it seems like they can be pretty resilient if there is no major internal damage.
Just best to be really careful with the little critters when they're too young to scramble (groan) from danger.