Once your license for Restrict plugin expires and you decide not to renew it, all of the premium features will stop working. Also, you won’t be able to receive any further updates nor to access premium support.
Basically, you will only have a free version of Restrict which means that you will still be able to restrict the content on pages or posts but premium features such as restricting access to partial content, widgets, menus, login forms, etc. will stop working.