You could get or make a hog house which they hog might choose to use for hibernation. Lots more information here:
Some people continue to leave a bit of food out during the winter. Hogs tend to emerge for short periods during hibernation and even move nests. But also not all choose to hibernate, so keep an eye out and if the hog is still coming out for food, continue to offer food. Also make sure there is water available all day every day.
Good luck, I hope the hog continues to do well.