If you accidentally delete the CRM organisation unit in AD and don't have a backup of your active directory (which is never a good idea), you may think looking at Microsoft's documentation that there's no way of ever seeing your data again. No so.

If you follow the Redeploying CRM 3.0 document (MicrosoftCRMv3Redeployment.pdf) in the RedeploymentTool folder on the CRM CD you can re-install CRM and create a new OU.