I was thinking they'd be returned to Gox, as Gox would need them to reverse all the broken trades. Gox will eventually come to a point where after they've reversed 99% of the broken trades, there will be some missing $ and BTC due to withdrawals (like Kevin's) preventing them from reaching 100% reversal. They might end up having to plug those holes with their own money to just leave a few trades unreversed I guess.
That. Cost of doing business. (and failing)