The following knowledgebase will help you to remove completely orphaned Domain Controller
1.Use the following knowledgebase to remove common Domain Controller settings
from the Active Directory.
Note 1: : You may need to seize the FSMO to alternative Domain Controller
Using Ntdsutil.exe to transfer or seize FSMO roles to a domain controller
Note 2: You may need to configure a new authoritative timerver in the domain.
2. Remove old computer account by using "Active Directory Sites and Services" tool.
3. Remove old DNS and WINS records of the orphaned Domain Controller.
4. Use "ADSIEdit" to remove old computer records from the Active Directory:
a. OU=Domain Controllers,DC=domain,DC=local
c. CN=Domain System Volume (SYSVOL share),CN=File Replication Service,CN=System,DC=domain,DC=local
5. Force Active Directory replication by using "Repadmin.exe" tool:
Using Repadmin.exe to troubleshoot Active Directory replication