If a head injury is involved, I don't know if a plant can save him. If he is struck in the head hard enough that it will be fatal, I'm not sure if there's much they can do for him. That's brain damage there. I don't think a flower could help to be honest.
But if the hail piece had some kind of virus or bacteria (I think they can exist in the ice, but I could be wrong) and he gets sick as a result of that, then that could probably work and give a reason for the gang to find a special flower.