Good question, as you know full well, I'm not a normal sane person. So, no I probably wouldn't expect you to keep those files in perpetuity, unless I'd specifically paid you to do so. Other people may assume otherwise though.

I would've said some clause in your contract that states that files are kept for up to 1 year (maybe), after that there's no guarantee you'll still have them.

The disc you gave me has been copied onto my laptop and ReadyNAS the day I brought it home. I 'think' I know where that disc is now, but I'm not 100% sure.