As broad leaved evergreens these Viburnum davidii have been very compromised by both the heat and intensity of the sun and drought. These leaves are dead. I expect many of these ill-adapted evergreens to die. Many woody deciduous plants have a greater ability to recover from this, because shedding their leaves due to stresses like drought and freezing is within their normal range of responses. In a sense, there is less of a separation between leaf and stem tissues of evergreens. In them this kind of damage to leaves extends into the woody structure of the plant.