A few things I've been pondering:
1) The entirety of the "coins" were not liquid. In fact, a small fraction were. Take a look at Gox's order book. 39k to $1 billion. Yes, that's not the full story, but to suggest that 750k coins were available on the market to begin with is absurd.
2) Presumably a majority of fiat on Gox was intended to be invested in BTC (as opposed to being withdrawn as fiat). That's a very considerable sum of fiat lost specifically by those with the ability to drive price performance.
3) While the markets can easily be moved by whales, the average investor is necessary to push up price past a certain point. What kind of fallout could we see from the Gox closure, in terms of "fresh fiat"? What time frames are we all talking about here?
I questioned the 750,000 BTC figure too. It seems an order of magnitude greater than I imagined. For this to be true, I must assume that a great deal of investors were using MtGox as a wallet. MtGox had 1 million customers, right? Stick 750mBTC in each account and you get to 750,000 BTC, so it's not inconceivable. Perhaps the value in GoxBTC dwarfed the value in fiat because of the "wallet effect."
I think the average bitcoin speculator invests a small percentage of their portfolio in bitcoin, say 2%. So Joe Speculator has his entire stash of 3 BTC at Gox ($2,000) and $98,000 in other financial investments. MtGox goes bankrupt. Joe loses 2% of his net worth, but 100% of his bitcoins. If Joe still values bitcoin in the same way, and if he acts logically, he would immediately rebalance his portfolio by converting 2% of his other investments into bitcoin (this would produce new demand).
But probably Joe is mad for a while, cursing bitcoin, but knowing deep down that bitcoin was not to blame. Bitcoin start to rally again and he decides to give it another shot. Bashful this time, he invests 1% of his portfolio and moves the coins to cold storage.
In conclusion, if MtGox lost 750,000 BTC along time ago, I think the net effect (after anger fades to acceptance) will be an increase in demand and a decrease in the effective bitcoin supply.