The clipped box bushes on our front courtyard came through the cold winter variously. Some look completely unscathed, but two were à-peu-près mort, as our neighbour Edouard noted. He said they weren't quite dead, but I needed to prune them hard, back to where the new shoots were coming underneath. I forgot to take before photos, but basically all the visible leaves were yellowy brown and the bushes were the same size as the green ones.
Hey ho - 10 plus years of growth into a ball about a foot in diameter, down the drain in minutes. I don't suppose it will take more than a couple of years for them to catch up again though. After all, they now have very little top growth and a substantial root system. I've fertilized and will try to keep the water up to them (one thing this weather will help with...)
I'm also having a lot of trouble with ant colonies moving in to the bigger pots. They really cause the plant to slow down, and then start to die off, I guess because they are disturbing the roots constantly. It's not obvious that they have moved in until the plant starts looking sickly. I'm trying to keep the soil too moist for them, but I don't think it's working (I'm not consistent enough).