Those "bitcoins" from Gox are never getting out.
They don't have to get out.
Mark can easily just sell them.
Either way. Shorting bitcoin NOW is the way to go.
If Mt.Gox will completly default -> price will drop hard
If Mt.Gox will allow withdrawal of bitocoins -> price will drop hard
Either way, we will go down to 100-250$ per bitcoin and stay there till mass adoption really kicks in (2-5 years).
Why do you assume Mark (and the people buying now if Gox does allow withdrawals) will suddenly want to sell? Mark already has a ton of coins of his own, by your logic he should be selling those.
If you think price is going to rise in the future, the rational thing is to hold regardless of the price you bought in at.