Remove Child domain

I have a network that has a child domain that because of some mistakes made with DNS or Active Directory so I want to remove it, and get things cleaned up. I am planing on deleting the site and Domain and records from DNS. I have tried to correct the DNS but I need to get this corrected ASAP. This child domain was set up as a test domain, but because of two many hands and not enough knowledge it is messed up. I want to get this cleaned up, so what problems would this plan
create? Or I am open to other sugestions on how to correct this, but I need the fix to be quick and sure.