I'm sorry for your loss. Fireworks are most definitely NOT my favorite thing. They terrify my dog and cats and I was worried about my hens as well.
Last night I was outside frequently, reassuring the girls about the noise. They seemed to be handling it (my neighbors' grandkids were setting them off in the yard right next door) fairly well but were hiding out in the deep brush of the garden. The one I was most worried about was the caged Australorpe (her monthly broody time) but while she was in alert position, she also did well.
But I have heard of chickens who have died due to the stress of an unexpected loud noise. Perhaps since here in Colorado they've been setting off fireworks for the past week (and they'll continue for another), the noise wasn't unexpected.
Mary