You don't need a catastrophic loss of human knowledge for this to be a problem. Running a piece of software written in the 80s, even with the source code available, can be quite a challenge. Support for some features of the current SQLite format might deprecated, then removed, over the next many versions. Or perhaps a subtle bug is introduced that renders certain ancient versions unreadable (https://news.ycombinator.com/item?id=15531489) and sticks around for long enough that you end up in a situation where you need to invest very significantly in software archaeology.