Error Operation Failed, failed to leave windows domain:

1. Login to your ESXi via SSH. Create a local group with exactly the same name as the orphaned group (case sensitive). Hint: Type EXACTLY what shows up in the error message when you attempt to unjoin using the Web GUI.
2. /usr/lib/vmware/busybox/bin/busybox addgroup ‘DOMAIN\\group^name’ **Note the double slash**
3. Now unjoin it using Web GUI or VCENTER
4. Remove the local group afterwards:
5. /usr/lib/vmware/busybox/bin/busybox delgroup ‘DOMAIN\group^name’