We will automatically convert all your helpcenters to free tier when your subscription expire. Your helpcenter data remains intact and live on free tier. 

Keep in mind that if you are hosting your helpcenter on custom url (pro feature) like help.onvoard.com, you should update all links to the default url like onvoard.pointanswer.help. When a helpcenter is on free tier, custom domain url like help.onvoard.com will no longer work.