It's probably dead, of rot. There is a small chance you can save it. Cut off all the dead parts into green tissue. Sanitize the blade between cuts with 10% bleach solution or a flame. If any living rhizome remains, let it dry for a few hours, then set it on top of some damp sphagnum moss or damp perlite inside an enclosure. Keep the enclosure warm and humid. It may make new growth.
__________________ May the bridges I've burned light my way.