Hydrangeas, while always hungry for some water in our daily 100-degree weather, are still tough plants. Depending on the plant itself, it may replace the damage with new growth once temperatures moderate or it mat delay things until Spring. Just keep the shrub away from deer as they like to much on all hydrangea varieties, except the hairy leaves one (maybe the leaves taste odd with the hair
. You can also apply (ie spray) products to keep deer away but those have to be re-applied after it rains. And considering they are warning that El Nin~o rains will come back in the Fall, I am not sure if other solutions might be more useful (a strong chicken wire cage fat away from the leaves or dogs).