I actually have an identical situation here and I'm in Zone 6b (PA). Those pots can be expensive. What I would do is tip out the sedum and put the plants somewhere for the winter outside, then turn the empty pot upside down, near a foundation wall or under some sort of cover (I usually roll mine into the unheated garage). I just wouldn't want to take a chance leaving it full of soil/plants outside. Once that freeze/thaw cycle starts (I hear you!) not only could the pot split but it could also start to flake apart. (I had both things happen to me.)
