A couple of things to check out. There’s no rust on the underside or on the body – it’s in very good condition. To the best of my knowledge, there are no mechanical faults, apart of little wining noise from the diff, but nothing to worry about.
The wheelarch chrome embelishers will be hiding something and diffs can be fairly expensive C-£250+.
I agree with Dieseleman WRT the wheelarches and diff - but for a 650 quid 200k mile car I think I'd live with those issues. Unless the diff is really loud and clonking like mad I'd imagine it'd last a good few more miles yet.