In my experience, source code tends to survive forever. Things outside it don't, whether through attrition via document retention periods, the IT department not

In my experience, source code tends to survive forever. Things outside it don't, whether through attrition via document retention periods, the IT department noticing nobody uses that document archive and shutting it down to cut costs (not before being told "nobody uses that!"), or hundreds of other possible causes. I've worked on code older than I am and those little comments that probably should have been design docs were a godsend. Nothing else had survived.