If you back up your stories as images, videos, and .pdf files, you'll be able to access them again if you delete and reinstall the app. If you transfer your backup files to a new device, you'll be able to access your stories when you add Unfold to that device.
Your stories aren't stored on Unfold's servers, so it's not possible to restore or recover past stories if you haven't backed them up.
You can restore Unfold subscriptions and one-time purchases of template collections regardless of whether you've backed up your stories.