I'm sorry if we misunderstood you. On Windows, Boxcryptor is always working with the encrypted files locally stored on your hard disk and not in your cloud. As a convenience feature, Boxcryptor automatically detects your installed cloud provider's folder but this is not a requirement. You can also manually add any folder on your computer as a location in Boxcryptor.
So even if you don't use your cloud anymore but still have your encrypted files stored on your hard disk, you can add manually add the folder with the encrypted .bc files as location in Boxcryptor to decrypt and access them. The encrypted files are not coupled to your cloud provider.