If you have a group of communications that are about to be processed in Core iQ and you choose to deactivate the template, these items will not leave the platform. Core iQ will check the system first to see whether the template is Active; and if it is not, then the communications will fail to send. This is a great forcible way to keep a template from leaving Core iQ if you ever find an error that needs to be fixed.
To be safe, it is best to completely clear the campaign using the Clear # Unprocessed button in the Outbound Communication Status area before reactivating the template. This is because Core iQ will attempt to retry the failed items for up to 4 hours after they failed initially, so reactivating the template may still allow the campaign to process.