Thanks to a lack of digital back-ups, an estimated $5 billion in student loan debt could essentially disappear. Last month, the New York Times reported on a series of lawsuits brought by financial institutions against former students who have defaulted on their loans. Some of the suits were dismissed, and all of the student’s debt erased, because important physical documents proving loan ownership had gone missing. No one can prove who owns the loans, meaning a judge can rule the student doesn’t…