Since Telerik licenses are perpetual, you are allowed to continue using the products even after the 1-year subscription expires. However, you will be using the last product version  released before your license expired. You will lose your access to new functionality and updates for new technologies. You will also have to use the online forums for support.

If you wish to preserve your access to product updates (new features and fixes) and dedicated ticket support, you need to renew your license - https://www.telerik.com/purchase/license-renewals. 

The following article is also helpful: https://docs.telerik.com/devtools/aspnet-ajax/licensing/old-versions-support-policy.