If a server, running Active Directory Connector crushes or is decommissioned from the network without first uninstalling ADC you can no longer remove this ADC through the ADC snap-in. You can see it in the snap-in but there is no option to delete it. Here you can see how to remove such ADC by using ADSIEdit:
I just finished the "Upgrade from Exchange 2007 to 2013" Part I screencast and must tell you that it is extremely well done! I found no variances between the video/script and what I experienced. At the end of Part 1 ...
Bob Duffett, Priority Software Inc. ...more...