If I take out the existing Domain Controller and install a new Windows Server 2008 R2 Domain Controller using the same domain name and all of the workstations would use the same logins, will the workstations divert back to a default Windows desktop?
What is the goal? To get to a new domain? New DC? Or just revert everyone to a default desktop? You've asked your question in a slightly confusing way.
The desktop that the users see when they log in are tied to their user profile, which can be stored either locally (default) or on a server as a roaming profile that is downloaded at login. The user profile is tied to the user account. If you upgrade your domain or migrate the domain services to another DC in the same domain then the user profiles (and the desktops that they see today) will stay the same. If you migrate them to a new domain then they will have new user accounts, new profiles, and default desktops on first logon.
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