Another thing to be wary of is that a lot of sites will create title records with no items for electronic resources -- things that are only available online. Those titles need to be protected from a global delete as well.
This script seems to allow to exclude items by items type (biblio level item type). That would solve your concern. But you need to have biblio level item type which isn't always the case. An improvement of this script could also be done in the way 'protected' biblio records are protected from being delete. It could be done directly in the SQL query. For example, this query find all biblionumber of biblio records without items and which are not of item type AGH or PER : SELECT biblio.biblionumber FROM biblio RIGHT JOIN biblioitems ON biblio.biblionumber = biblioitems.biblionumber LEFT JOIN items ON biblio.biblionumber = items.biblionumber WHERE items.biblionumber IS NULL AND itemtype NOT IN ('AGH', 'PER');