I have to doubt that based on historic precedent.  I happened to have gotten serious enough about Bitcoin to use a typical exchange during the fortnight-ish the Mt. Gox was off-line due to their hack.  It seemed to have had a remarkably small impact on the actual valuations.  They were already in decline and continued in much the same trend once Mt. Gox came back.

If you are implying that Mt. Gox would lose significant BTC I highly doubt that.  They have way to much experience, skill, and money not to have a robust cold storage regime.  If they lose BTC it is almost completely certain to be an inside job.