> if you choose a library to implement some on-disk format, then that can cement things in. If the library becomes unsupported one very well may end up maintaining it alone, for example.

But, presumably, you used that specific format because you needed it. So, it makes sense that you take it over if it gets abandoned.

If the problem is that you didn't need that specific format, then you should rip it out completely when (and only when) that library becomes unsupported.