I believe that the Bitcoin market has already answered that question. The market seems to feel as if this is very risky, thus you see a 50% cut in the price of GoxBTC as opposed to BTC.
If MtGox had access to the coins they could just transfer them to other exchanges sell off and buy on their own and make crazy arbitrage.

Manual Bitcoin withdrawals should be available for larger orders. There is definitely something fishy about MtGox.