Demote a domain to a workgroup?

I work for a small company that is breaking up. We have a small WAN consisting of a just a few servers that make up our W2K domain, with three exchange servers, and three sites. In the process of selling these business I need to convert the servers to stand alone. From what I can see, we will lose AD all together. I guess my biggest question is: Is there a way to convert the users in AD to a workgroup, and keep their group membership intact? Will I have to rebuid the user accounts? Any idea howthis would effect my Exchange 2000 enviroment?
Any other considerations I may have missed?
Thanks a lot……..