Can toads survive winter hibernation buried only in rocks?

A pair of toads found their way into my basement's fire escape a few months ago. They were living fairly happily at first so I figured I'd let them stay in there, but then they began trying to burrow for winter. One toad vanished and hasn't reappeared, but the other tried to burrow in several places. It finally settled someone for about a week but today, during a rain, it emerged again. Since the floor of the fire escape is just rocks (no dirt, plant matter, etc) I'm not sure if it'll keep them alive. Should I relocate them to save them from freezing, or not disturb their burrowing attempts if they'd be able to survive? (: