The question, as always with markets, is how much of this is already priced in. The MtGox BTC price has diverged for quite some time and is currently at $115 which tells me that a lot of people are already assuming a low probability of ever seeing any of the money in MtG accounts again.
So, basically there are two scenarios and combinations thereof if they indeed lost all of the coins:
1) Most of a complete loss is already priced into the general BTC market and nothing much happens.
2) Once this gains more (mainstream) attention and the general public realises what has happened, the trust BTC had been able to gain evaporates and there will be strong sell-off.
I don't think it's possible to say which one it will be.