If you have made a mistake with your contact imports, MCA Suite will allow you to undo the import within 14 days.  After a successful import, the last 5 imports will appear as shown in the screenshot below.  Click the 'Undo' link and the process of unimporting will start.  You will receive an e-mail once the process is complete.  Any duplicate contacts that were found in a later file will not delete the contact from the system and changes will remain on that contact.  Only undoing the original file the contact was initially imported with will delete that contact.