If my Delivery Restrictions plugin expires, are blocked pincodes still blocked?

No. Pincode blocking is only enforced while your store owns the Delivery Restrictions plugin. If it lapses, orders from any pincode are accepted, even though your pincode list and messages are still saved.

When you renew or activate the plugin again, the saved settings take effect again straight away. You don't need to re-enter your pincodes.

Until then, check new orders in Orders → Manage Orders before shipping. If one is outside your area, open it, set the status to Cancelled with a reason and click Update Status.