After a full synchronization and incorrectly installed connection filters a lot of users have been removed from User Profile Store. After that, users have been restored using the import option.
If the photos are still present in the My Site Host User Photo library you may have luck with Update-SPProfilePhotoStore. The rest of their data is stored in the Profile Database and unless you have a backup is lost.
In the sitution you are, i think best option is restore the UPA. So now it is depend if you have the backups SharePoint. You should have either farm backup(including services) or UPA content Database.