You should probably cut back all of the branches with brown, curled leaves, as they are not likely going to recover. This may mean cutting them all the way back almost to the ground. While leaf curling and wilting like this can be normal for several evergreens (Viburnum, Leucothoe, Rhododendron) during periods of cold weather, when the leaves turn brown and haven't uncurled in warm weather, they have died. Whether the branch itself (along with its dormant buds) has completely died as well is harder to tell just from a visual inspection, but typically when damage is this drastic and extensive, it has.

There's a tiny bit of healthy-looking growth at the base of at least one of the shrubs in one photo (hard to see with the Pachysandra beneath it), so regrowth from the roots might be possible, though it will take years to reach this size again. Otherwise, it's simplest to just replace both plants and start with healthier individuals, whether another set of Viburnums or a different shrub species.

What the original cause of dieback was is difficult to determine, though it would not have been winter temperatures. It's possible damage was cumulative and not acute, even if the final manifestation of symptoms was relatively sudden. Viburnums are prone to Botryosphaeria canker when under stress, especially from drought or under-watering. (Our page on this fungus focuses on rhododendron because that's a common host, but it applies to other shrubs as well.) Viburnums can also contract various root-rotting fungi when over-watered or when drainage is poor. Frustratingly, symptoms between these two causes are nearly identical. Since the Pachysandra carpet seems to be thriving, too-dry is more likely than too-wet, the latter of which probably would have caused root rot on the groundcover as well. In comparison, Pachysandra does have decent drought tolerance, though it also could have simply had better access to limited moisture during periods of insufficient rainfall in summer or autumn.

All of these fungi are ubiquitous in the environment, so there is no point in using a fungicide; plus, once infected, a shrub can't be treated to reverse any damage already done. Still, fungi only tend to infect plants already under stress from their growing conditions, so replacement plants won't necessarily be equally vulnerable to infection if they can be periodically monitored for watering needs. (Soil moisture being the most common cause of plant stress in home landscapes.)

Miri

As always thank you for your quick and in depth response. I’ll cut them back over the weekend. Do you think if they appear to be alive and healthy in a month or so, I could try to dig them up and replant in a different area?

Steven

You're welcome.
You might be able to transplant them if they appear to be recovering, yes. Anytime between now and early autumn would be fine to move them to another location if you wanted to relocate the shrubs.

Miri