There are programs which can scan drives to find keys. I modified a simple one that has found 500,000 potential keys on an old drive image I had archived. Most of those are going to be duds (not a key, just coincidentally the same series of header bytes), a very small number will be real keys that have been used and now have zero balance, but if I'm really lucky it might find something odd that got lost some years ago. I've been using Bitcoin since 2011 so who knows. I'll find out in a couple of days when it finishes importing them.
