You may see an error like: [Domain] points to the [site] which does not exist. Please contact the domain administrator. or "site not found" or "we were unable to locate the site".
This issue has appeared on the Google Sites Help Center forums lately since Google, as part of their sunset of Classic Google Sites, is actively deleting sites. Some has created hundreds of webpages or spent many hours on their Google Sites website and might be in a bit of a panic. Don't worry, let's help you find your deleted site in a couple of places.
Deleted Sites Dashboard - https://sites.google.com/site/sites/system/app/pages/meta/dashboard/deleted - check this dashboard to see if you site was deleted or not. You probably won't be able to restore or recover it here though.
Classic Sites Manager - https://sites.google.com/classicsitesmanager - check this database to see the status of your Classic Site, try to convert, or download via Google Takeout.
New Google Sites Landing Page - https://sites.google.com/new - Here is where most access their New Google Sites. Complete a search of your Site Title here to perhaps find the automatically converted, or migrated, site.
If your site was automatically migrated to a new Google Site, you might need some help fixing up your intranet or business website. I've seen hundreds of converted sites in disarray and if you can't stand it, contact us for support.