Scratch bark along those stems/branches from tops down toward the base. If there is no green beneath the bark, that part of the plant is dead.
What advice to have given when the chemical contact occurred: Immediately hose off all the foliage, through which most contact herbicides are absorbed. Next, upon visual observation of leaf wilting/death, cut off all the branches with foliage - so that herbicide can't be translocated further into the plant. This would trigger activation of dormant buds, which could then grow out into new stems and leaves to begin the process of photosynthesis to support new growth and plant survival.
Depending on the type of chemical, if it has been translocating throughout the plant for quite some time, there is not much good to be said - depending on what kind of chemical it was. IF it was only a "burn down" defoliant kind of chemical, your shrub may have the best shot.
