If you want to try to keep the plant going, you can restart the healthy parts that are left as cuttings. Use a clean knife to cut across the stem through healthy tissue above the soft part, allow to dry out for a couple of days, and plant in soil.
To figure out what went wrong (and to proceed with a healthy cutting), it would be helpful to know what kind of exposure and water the plants were getting. Was there something in particular which seemed to trigger the problem?
