All of our licenses are perpetual (ie one-time fee) licenses and come with 12 months of software updates and technical support. After your license expires, you'll have the option to renew with a discount but it is not required to continue to use Froala on versions that were released prior to the expiration date.
For example, if your license expired 10/1/19 and you chose not to renew, all version released prior to 10/1/19 would be permissible but any versions after 10/1/19 would not be unless you chose to renew for an additional 12 months of software updates.
For further clarification, feel free to email support@froala.com!