Always backup Domain, SYSVOL etc.using processes according to Microsoft Best Practices. This is meant as a disaster recovery process for small environments that did not implement backup processes and did not run a secondary domain controller that need to recover Group Policies from files
1) Create new, blank Group Policy
Using GPMC.msc create a new, blank GPO with the same name as the original.
2) Overwrite Group Policy Data
a) Record the Unique ID that was assigned to GPO created in Step 1
b) Copy Machine, User and GPT data from original GPO
c) Paste data (overwrite) into the folder assigned to GPO created in Step 1. The folder is named the same as the Unique ID recorded in Step 2a
3) Fixing Group Policy Settings Preview
Note that after completing Step 1 and Step 2, even though the GPO settings are available within Edit, the Settings Preview shows No settings defined
a) Edit GPO, browse to any unconfigured setting and open it. Tick and untick Define this policy setting and click OK
b) If your GPO contains any Preferences browse to any one of them and simply open it and click OK
Settings Preview should show settings
4) Fixing Group Policy Permission
Unfortunately following this process does not restore the original permissions, this has to be added back manually.