Even you restore files from time machine , passwords are encrypted they can't be physically read by the administrator , the autofill box is to be checked and iCloud Keychain box is to be checked in system preferences ( if there are any issues in iCloud Keychain if you click on reset iCloud Keychain all passwords will be lost and that is to be done in very rare scenarios .
If you try to import passwords from iPhone to Mac the article is posted , if you are not using iPhone and only Mac , the iCloud Keychain is set up and passwords are stored inn keychain access .
These passwords can be read by opening keychain access , double click on web mail address , enter the admin password and click on the box show passwords ( but in your case the number is more than 500 , that is very time taking job ) .