I'm pretty sure I have seen a user with a user name like
user1234567, that had a grayed out name link, but was active.
(I did not find the example)
From Some User is Shown As Greyed Out, I understand that grayed out user names indicate deleted user accounts.
The last comment from the user was one hour ago - it feels improbable that he had been deleted in that hour.
(I noticed because I wanted to comment on something for him, but was unsure whether he can communicate at all.)
Is there something special about deleting anonymous users? I assumed an anonymous account is based on a cookie in the users browser, so even if the user lost that cookie, we would not notice.