Once the government seizes assets of MtGox, you will lose whatever you had in there. If you think this is impossible or that governments never confiscate, then by all means, leave everything you have in there.
If you think there is even a slight possibility that they will, then you'd be a fool to leave anything in there for extended periods of time.
I'm in the latter camp. If there is anything I know, it's that governments are incompetent, and far more likely to take incorrect and drastic measures. MtGox going down would have an adverse affect on the Bitcoin market (the price would fall significantly) for a short period of time, then it would slowly recover over time, eventually surpassing where it was prior to the freezing of assets.
FDR confiscated US citizen's gold in the 1930's. People who owned gold were deemed "hoarders" and guilted into turning it over. Many did. After confiscating about 500 tons, it was sold to the Treasury who owes it to the Federal Reserve. Shortly after it was confiscated, the "fixed price" between dollars and gold that had remained the same for decades was modified in such a fashion that the people who held gold and never sold it were better off.http://en.wikipedia.org/wiki/Executive_Order_6102
Make no mistake, if MtGox goes down, those of us that don't keep our money in there are going to be better off than the ones who did.