If Gox continue to delay or imposes New quota on btc withdrawal, market will assume Gox is nearly insolvent. Price plummets.
I don't think that the hypothetical failure of MtGOX would have any immediate effect on prices. If they
are insolvent, the virtual coins and virtual dollars that are in their cllient's accounts do not actually exist, so they will not enter or leave the market. Traders who have their assets on other exchanges will not be surprised, and should not care.
Howeve, if the "oldest and most prestigious" exchange fails, it will probably be all over the mainstream news media, and will scare more potential investors away from bitcoin. Since I believe that bitcoin is a terrible investment, I think that will be a good thing; but it will depress the price even further over the next few weeks.
A major news agency already sent out news that "price of bitcoin drops 50% in a few hours". Not surprising since many chart sites still show MtGOX's price by default, or put it at the top of their menus.
If MtGOX is
not insolvent, when they resume withdrawals most clients will probably take their coins to other exchanges, and move their money to safer investments. That will probably have an immediate negative effect on the price.