You can open this page without signing in. Deletion still requires you to prove the account is yours.
Deletion uses the same service as Settings → Security. It is not reversible from the product. You confirm by typing DELETE.
When deletion completes, it removes:
If the local account is removed and the sign-in identity cannot be deleted, deletion is incomplete. This page shows that error and does not say the account is fully gone. Support has to finish removing the sign-in identity.
Checking whether you are signed in…