Hi Wheeler,
Thanks for reaching out with your Total upkeep questions. This is a very unfortunate event, the encryption key is absolutely needed in order to reverse this setting.
When you create your key the plugin prompts you to save it and notes the importance of why you should. The only way to recover it would be to log in to the origin site and obtain the key from your web server backup if the file still exist.
I hope you’re able to salvage the backup. Please let us know if there’s anything else that we can answer for you.