Maybe. It happens often here because our Winter temps fluctuate a lot. Warm temperatures trick leaf buds to open early but there is little one can do about that. A cold front could easily zap them and force the plant to go back into dormancy. Generally speaking, it should not kill the plant, especially the roots which are protected by the soil and mulch. Hydrangea Anomola subsp. Petiolaris is quite tough and will develop replacements later in Spring. Keep the shrub mulched with 3-4" of any type of mulch and, when exposed to warm temperatures for a while, water the soil on the night prior to cold frigid temperatures.

Thanks, luis! That's very helpful. Stupid me forgot to mulch in the fall (ok, I knew we had wet winters and was worried I'd cause everything to rot so I used that as an excuse to be lazy), but I have some plant-warmer blanket things I might put on just before severely cold weather. We haven't gotten any temps cold enough to threaten the petiolaris from what I've read. Good to know it will create replacement buds.

FWIW, the buds on hydrangeas will often be present when the plant enters dormancy - the buds on my shrubs are visible as soon as the old foliage drops. The appearance of buds does not necessarily mean it is beginning to emerge from dormancy - winter buds are present on many deciduous shrubs and survive the cold undamaged. It is how many plants are ID'd during the winter months :-) The buds that are visible in winter tend to be mostly foliar buds......flower buds are nascent but much slower to develop and become visible.