Abort the program, send a fail code back to the software.

So in the restricted world of 80s software without much ram/disk room for robust error handling the in practice difference is usually nothing

It doesn't matter. The appearance of the message itself usually meant the drive/disk was dead and there was nothing you could do about it.

Even worse, programs almost never handled this gracefully so if you were trying to save your work it was effectively lost and you might as well ctrl-alt-del, even if you had another disk or drive (already attached).