If bitcoin cant survive the loss of Mt Gox, it doesnt deserve to survive. Sure there will be a PR blowback, but I think it would be one the best things that could happen for bitcoin to not have an easy way to cash in or out, for a while at least. That would really force everyone to use it as banter, as the only way to obtain bitcoins would be mining or conducting trade. The only way to unload your bitcoins would be buying stuff with bitcoins. Circulation of bitcoins would drop dramatically, but actual trade would likely spike and me thinks thats precisely what bitcoin needs.
If the only way to use bitcoins would be to trade them for good or services, how do those goods and service get purchased to make the trade? There is one, perhaps two degrees of separation at all points in the chain between bitcoins and your national currency.
Then there is the question of why anyone would want to use bitcoins if that were the case. Why trade in a market with a few hundred, possibly a few thousand participants, where using a conventional currency means you can trade with many millions?
Merchants love the no charge back feature of bitcoins, but customers hate it. On another BitcoinTalk forum there's debate on whether a very cheap FPGA miner solution for US$499 is actually legit. Those people who have signed up and paid the money all say 'if it's not legit, I'll get my money back through my card/PayPal'. I wonder if they would be so keen if they had to pay up in bitcoins.