2 Remove Last DC from WinServer 2008R2 Core

dcpromo /unattend:C:\Users\Administrator\DC.txt

[DCInstall]

UserName=benpdom\Administrator

password=* <The password for the UserName account> Specify * to prompt the user for credentials during the installation.

administratorpassword=<The local administrator password for the server>

removeapplicationpartitions=yes

removeDNSDelegation=yes

DNSDelegationUserName=<The DNS server administrative account for the DNS zone that contains the DNS delegation>

DNSDelegationPassword=<The password for the DNS server administrative account>

IgnoreIsLastDCInDomainMismatch=yes

IgnoreIsLastDNSServerForZone=yes

IsLastDCInDomain=yes

RemoveApplicationPartitions=yes

RebootOnCompletion=yes

Reference

http://support.microsoft.com/kb/947034