These are all valid concerns and I certainly don't want to marginalize them. We will be creating a standalone client/utility, but the priority is lower than other things, at the moment.
You do need a Premium subscription to use Encryptor. In the scenario where there is a short odrive service down situation (which has not happened, thus far), the odrive client would still work for a while to decrypt your files as long as you had already gained access to the Encryptor folder and odrive had confirmed your Premium subscription prior to the service becoming inaccessible. I just tested this myself by blocking access to the odrive service on my system and verifying that I could still download and access my encrypted content. It will not work indefinitely, because there will be session expiration/validation that will need to happen periodically (times will vary depending on the storage service), but it will be long enough to deal with a temporary comm break.
Keep in mind that all encryption/decryption happens exclusively on the odrive client (there is no cloud component needed for it) and the odrive client will communicate directly to the remote storage for access to that data.