OK so it isn’t really dead, but it isn’t necessary anymore. I’ve run into this out in the field a few times recently, it would seem we didn’t get the word out on this very well.
In older versions of Windows (prior to 2008) you had to use a tool called “ntdsutil” to forcably remove dead DC’s (or DC’s that were forcably removed using dcpromo /forceremoval) Here are some screenshots of that process.
As of 2008 this is no longer necessary. Simply deleting the account from the “Domain Controllers” OU will do the trick. Alternatively you can delete the DC from Sites and Services. Few extra steps but it works.
For more information please refer to this technet article.
And before you ask, no. To my knowledge there are no plans to actually remove ntdsutil.