Alternative Solution after Sync Option is disabled

Thanks for your suggestion, jcgonzalezmartin and Brad Warrender.

(1) With Files OnDemand you have not to worry about your usesrs synchronizing a lot information coming from SPO Document Libraries.  

Currently users mostly use windows 7 instead of using windows 10. Files OnDemand may not suit to be introduced to the users.

(2) To avoid your employees make incorrect use of your corporate documents, there are some advances features in Office 365 that can help you. Take a look at features such as IRM, Azure Information Protection and others

We are still seeking on AIP solution and taking time to process and coming out the policies. For this moment, we have to disable the sync option until DLP is in place (may wait until mid of 2019).

(3) Document editing from SPO sites: I think you need just to teach your users about how to save documents in SPO and open them from there

The only way is educating the users to open through web browser or using ms office and save as to SharePoint sites. The users may raise the concern in terms of user experience as they are familiar with the shared folder styles or oneDrive sync to local.