If it was planted in October, it was getting into the cold season. Watering it while it is still adjusting to its potting situation plus the timing of your watering on a cold snap with that drafty window may have caused that middle part to wilt.
I think it can still be saved..if it were my plant, and Spring is coming about anyways, I would pull that plant out to inspect the root section. If it is soft and mushy, chop off that portion and let it callus for a few days to a week. Consider putting it in a smaller container too, I think what you are using is way too big for now. Also try to add more pumice into your soil.
As much as possible I try to do succulent repotting in Spring.
