If your custom domain expires or is removed from the service, any short links associated with it will stop working. Visitors will no longer be able to access those links until the domain is renewed and DNS settings are configured again on your side.
Once the domain is active and correctly pointed to the service, you can re-add it and resume using it for your links.
You can also set up a custom 404 page for your domain. This allows you to control what visitors see if a link is inactive or unavailable, helping you maintain a consistent experience instead of showing a standard error page.