Honestly, those will probably be fine above freezing. I have heard of some recovering even after forming ice crystals. When you consider how easily these can spread from just a small piece of surviving tissue it is not surprising that even such extreme cases aren't always a loss. I just don't think it's worth paying overnight shipping for a coral that is probably worth less than the packaging. If you pack them well, they will probably survive, and if you insulate them well, they are almost guaranteed to live unless they get stolen or totally pulverized somehow. Same applies to most soft corals and corallimorphs as well as zoanthids.
Make sure to ship them "dry" (in a container with near 100% humidity but no water to slosh around. Use wet paper towels or newspaper to keep them from bouncing around but don't wrap the coral tightly, just enough to keep the inside humid while allowing it to breathe) they tend to ship better dry. Most corals are well adapted to being in the open air for extended periods and their response to shipping stress often kills them faster if they are in stagnant water. This stress response is an adaptation to low-tide or seasonal tide environments where they often spend half a day out of water and in the baking sun, and it seems even many typically deeper water corals have this same response. They coat themselves in mucous and stop wasting their energy. The mucous protects them from drying out but will foul the water if they are in water. They also seem to be surprisingly resistant to a wide range of temperatures (so long as the swing isn't too fast) both cold and hot.
