Even after a paid subscription expired, you can use all previously paid features of the Tag Groups Premium plugin. You won’t, however, be able to install updates or use our premium support unless you extend the subscription.
Since WordPress issues a new version of its core package every few months, it is recommended to regularly update all plugins to an officially compatible version.
You can switch back to the free plugin anytime. Please note, however, that naturally all changes you made using premium features cannot be transferred to the free plugin.