I understood correctly that you upgraded to 2.0 on Windows, imported your Classic Folder und want to go back to Classic to use Boxcryptor also on Mac again?
1) The 2.0 Importer does not delete the Boxcryptor Classic Folder. If you haven't deleted the Boxcryptor Classic Folder yourself, it should still be available.
2) If you deleted the Boxcryptor Classic Folder, you can try to use the "Undelete" feature of your cloud storage provider to restore it.
3) If there's no chance to restore the Boxcryptor Classic Folder, you can install Boxcryptor Classic on your Windows computer in parallel to Boxcryptor 2.0, create a new Boxcryptor Classic Folder and copy the files from the Boxcryptor 2.0 Drive to the Boxcryptor Classic Drive.
Hope I could help. If you need more information, just ask.