Cold weather in the 20s will likely zap the foliage of newly emerging clematis depending on how protected of an area they are in. The roots however will be fine and new growth should emerge with time. Clematis getting zapped by frost in the spring is no different than them getting zapped by frost in the fall. It doesn't kill them, it just kills the top foliage. In the fall/winter however, the plant gets put into dormancy due to the increasing amount of cold weather and decreasing amount of daylight. In the spring, the plant just gets set back but the returning warmth and increasing day length just stimulates new growth.

Okay, that's what I figured. Thanks. :0)