This article will show you how to delete an Exchange Server 2007, 2010 or 2013 that cannot be recover or restored and it is offline for good.
To remove the server record we need to use the ADSI Edit utility.
To start open ADSI Edit and open the Configuration Naming Context with the default path
Go to the Exchange server entry at:
CN=Configuration, DC= Domain_Name ,DC=com, CN=Services, CN=Microsoft Exchange, CN= <Organization_Name>, CN=Administrative Groups, CN= Exchange Administrative Group (name), CN=Servers, CN=< offline Server Name>
Right Click on the server and delete