What Pro adds

• Loop grid: lists of posts or any content type, with a template for each entry and page numbers.
• WooCommerce widgets: products, add to cart and a cart link (WooCommerce must be active).
• Display conditions: in the settings of any element, show it only to logged-in or logged-out visitors, to some roles, or between two dates. Hiding on desktop, tablet or phone is free.
• Advanced template conditions, and export and import of templates between sites.
• Custom fields in dynamic tags: {meta:field_name}.

If your licence ends, nothing breaks: what you built with a Pro feature stays and keeps showing. You just cannot add or change Pro things until you renew.

With a full-page cache, conditions based on the visitor need a cache that tells visitors apart.