Alot has been orphaned here. The user's profile is underneath their previous GUID, which has both registry settings and the directory on the local or remote disk secured by permissions tied to that GUID. Leave the user's workstations joined to the orphaned domain until you need to cut each one over. Cached credentials should at least allow them to login and continue to work, assuming you're not using roaming profiles or folder redirection. Otherwise, you'll have to cut them over and the copy the files in their profile and if possible export and re-import some registry settings. How many machines and users are affected?