Before attempting to remove a domain from an AD forest, it is important to take the following into consideration:

1. Ensure there are no user accounts, computers, or trusts associated with the domain
2. Move any objects that cannot be deleted, as they must be in another domain before the domain is removed from the forest
3. Perform a forest wide search to identify any member servers or any other object associated with the domain
4. Backup any objects to be removed using the appropriate tools
5. Verify DNS and trusts are all configured correctly before the removing the domain.