To force the removal of a domain controller by using the command line in server 2008 core 

• At an elevated command prompt, type the following command, and then press ENTER:
  
  dcpromo /unattend /uninstallbinaries /forceremoval /demotefsmo:yes /username:<domain admin> /userdomain:<domain> /password:<DA password> /administratorpassword:<local admin password>
  Where:
  • <domain admin> is the name of an account that is a member of the Domain Admins group.
    
  • <domain> is the name of the domain for the domain controller.
    
  • <DA password> is the password for the account that is a member of the Domain Admins group.
    
  • <local admin password> is the password that will be used for the local administrator account on the server after AD DS is removed.
    
  The following example forcefully removes a domain controller from a domain named contoso.com, removes the AD DS server role binaries, and sets the local administrator password to p@$$w0rd:
  
  dcpromo /unattend /uninstallbinaries /forceremoval /demotefsmo:yes /username:DA1 /userdomain: contoso.com /password: DA1_password /administratorpassword: p@$$w0rd