After you as the admin publish a meal plan, your members have the option of personalizing the plan to meet their specific needs:

When you as the admin choose to delete a meal plan, or move it back to Draft mode, you have the option of allowing members to retain their customizations, or deleting those member plans in addition to the original plan you created.

If you allow members to retain their copies, they will no longer have the option to reset back to the parent plan, but they will have the option to completely delete.