There is a great option in Gmail to restore contacts to any previous state within past 30 days. If you made a mistake when import, merge or delete contacts then using this restore / recover option you can undo the import or merge contacts steps.
Login to your Gmail account, click on Contacts menu
Click on “More actions” tab and select “Restore contacts” option
Here you can select the time and restore contacts to specific days and time within past 30 days. Select specific time and hit the restore button.