is there something like bankruptcy protection?
Yes.
n who will pay him the bitcoins back?
Porbably nobody, but we'll have to wait and see.
n really has he lost all the bitcoins?
News reports indicate that he is claiming to have lost 850,000 of them. It is not clear from the news reports that I've read how many they still have.
even the coins at cold storage?
I'm not convinced that MtGox had a true "cold storage" system in place. Whatever they thought they were using for "cold storage" obviously was ineffective at protecting them from significant loss. My best guess is that they were running "fractional reserve" for a long time hoping to earn enough to replace smaller losses from months (or years?) ago, and were not paying attention to how large the reserve was. Given their apparent lack of attention to detail, it wouldn't surprise me if thefts caused that reserve percentage to shrink over time without them realizing how low it was getting.
It is not yet clear if we are looking at incompetence, negligence, fraud, or some combination of two or three of those.
