Hi Rusty 

Thanks for posting in the community! If you cancel your subscription you will simply be on a free account and continue to have access to your documents. However if you have premium shapes or features in your documents or documents that exceed the limits of a free account (3 docs 60 shapes/document 25 mb storage) you will be unable to edit them. 

Instead if you close your account entirely you will lose access your documents. If you wish to continue using them I would recommend downloading them in a format such as PDF. Note that your Google Drive backup is solely a backup of Lucidchart files (.lcd) which cannot be opened without your Lucidchart account. Hope this helps! Please let me know if you have other questions.