People have tracked the addresses where an entity (very likely to be MtGox) transferred funds to prove that they had lots of bitcoins, and they haven't been moved from that address since then.

If insider “malfeasance” is the true cause, it just boils down to “who is more patient, those who have lost some funds, or the guy sitting on 700,000 BTC and just needs to wait for this to blow over”?

It's still there. It didn't disappear.

If I delete my wallet and all the backups, it might still be in the blockchain but it's effectively gone forever because it can never be spent.