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Most potted shrubs will survive outdoors during winter, especially holly bushes; however, you can move them to a protected area, if desired, until the return of warm weather. The following article should be of some help to you:
https://www.gardeningknowhow.ca/ornamental/shrubs/shgen/potted-shrubs-growing-shrubs-in-containers.htm

There is no standard rooting hormone for holly. The real point of rooting hormone is actually more to be a fungicide. This will prevent rot from setting in. Any rooting hormone your local nursery carries will be fine for rooting holly cuttings.

This article will help you:
https://www.gardeningknowhow.ca/ornamental/shrubs/holly/propagation-of-holly-shrubs-with-holly-seeds-or-cuttings.htm

If it has been kept indoors, it will not be able to survive the cold outside because it has not been allowed to go dormant. You will need to bring it into somewhere warmer and keep it there for the winter and treat it like a houseplant.

If it has been kept outside, it has gone dormant and should be fine in the car for a few days, though I would wrap a blanket around the base to keep the roots a stable temperature and you need to remove it ASAP if the temp in the car will rise above 40F. It will be ok for a few days without water.

Once the storm is passed, place it in a sheltered location, like against the foundation of a building or in a shed or garage. If it will be in a location where it will not get water, water it once every two weeks. It will not need much water in the winter while it is dormant.

There is a pretty good chance that the plant will survive, as long as it only happens once. If it happens repeatedly, the bush will have a harder time recovering and regrowing the leaves, but 1x should not cause a healthy plant to die.