Bay trees are pretty tough, so yours must have suffered more than most, or it was already sickening, or weak. Is it in a pot? Was it well watered prior to the cold spell? Is it under the lea of the house, and therefore doesn't receive much natural prcipitation? If it's as bad as you say, it may be that its little spirit has moved on. Worthy

If it is frost-damaged, I would look at the stems. If the younger stems are still plump and green, it will come back easily come spring. if the young twigs are shriveled and brown, but the thicker stems still show moist green when nicked, slightly, then it likely will still come back, but more slowly. If the stems show brown insides as you nick deeper into the crown or farther down the trunk, it sounds bad--it may still come back from the base, but you will need a few mild winters to train it back into tree shape. A mild feeding in spring with a complete fertilizer will speed recovery, and so will placing it in a warm, sunny spot. Don't cut off any dead stems until it sprouts in spring--they will be protecting the live parts from further damage, if the cold comes back.

Still very early to say, wait till we put the clocks forward and the plants can get some light and (hopefully) get some warmth to get them going again.