Answer: This plant Carex buchananii is described in the Monrovia online listing as being hardy into zone 5 so it should be able to overwinter in your area. I would be very patient however as some sources describe it as needing extra winter protection (such as deep mulching) to come through winter in zone 6. (You may need to cut and paste the complete url into your browser to make it work correctly.)
If the remaining foliage is discolored and dry (or rotting) and dead, go ahead and remove it now to allow the sun to reach the crown and warm the soil there. Your local professional nursery staff may be able to give you a more precise time table for how long to wait and see. I hope it is okay.
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