I hope it recovers. Unfortunately air layering is asking for trouble with adeniums, it WILL rot. Air layering is for woody plants, not succulents. The way to propagate stems is to make a cutting, seal the end with 3% hydrogen peroxide and then leave it in a warm place until you see roots forming and immediately cutting the still-healthy stems was also the correct way to save it. Then you can place it in a small pot which has well draining soil and begin watering carefully.
When cutting rot, you need to keep cutting until there's no brown flesh remaining and then seal it with peroxide. Don't water it until you see leaf buds forming, which may or may not be possible that low down on the root