I'm am totally in favor of merging borrowers and deletedborrowers! I think the same could be said for most if not all of the deleted/old tables.
I couldn't +1 this more vigorously if I tried... I write a lot of reports for libraries, and I waste^H^H^H^H^Hspend more time writing clever coalesce statements in an effort to avoid MySQL's performance penalties for subqueries and unions... the results tend to be ugly and brittle.