Hello,
Once you delete the AD sync from SEPM, all the clients would report to the SEPM's default group in the next Heart Beat Interval.
To Delete the AD Sync, here are the steps:
* In the SEPM under Servers
* Right click on the server name and select Edit Properties
* Click on Directory Servers
* Select each server listed and click Delete
* Uncheck Synchronize with Directory Servers
* Click OK
* Wait for the database maintenance task to complete (happens at midnight)
* After a few minutes, go back to the Clients section
* Right click on the top OU and select Delete
The clients should end up in the Default group once they check in again.
Hope that helps!!