- As MtGox BTCs price drops relative to Bitstamp BTC, more BTCs will be bought/withdrawn on MtGox, and the cost to MtGox to make customers whole also goes up
This is flawed logic. The amount of fiat at Mt.Gox is fixed as people cannot withdraw significant amounts.
Assuming you are correct and Mt.Gox is short BTC then a low BTC price is ideal for them because they can replace their losses for less fiat money.
If nothing else, they can borrow against all the fiat noone can withdraw anytime soon.