Fix bad files and streams with ffmpeg so VLC and other players would not crash
If parts of the file reside on physically bad sectors, or for whatever reason, the OS cannot serve the whole file to FFmpeg, then naturally FFmpeg can't do anything about that. You should get a utility which can ignore those portions and write the salvageable parts to a new file, like ddrescue.

Now, if the file protocol is not the cause of errors, you can try

ffmpeg -err_detect ignore_err -i video.mkv -c copy video_fixed.mkv