Answer: If you're finding new growth at the bases of the plants, it indicates the roots are healthy which leads me to believe the plants either experienced a harsh winter or a lack of water to the extent that the roots could not support the tops of the plants. I think they'll come back, but it could take a few years. If you're looking for a faster fill-in, you may decide to replace your arborvitaes.
Best wishes with your landscape!
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