deep scratch on outside of game data

[D.D.D.]

Well unless he's played it in its entirety, it may or may not f-up on you towards the end (as data is written from the inside to out).
IIRC, there's no copy protection on it - I'd ask him to make a copy of it and if it fails on any data sectors, well, there's your answer. If not, that's a good deal~

Data portion of Keio is only about 65mb, so data is not going to be a problem.

So music skipping is still a possibility then if it's out far enough and the scratch is that far in.