You can't go to jail for losing $400 million, you can go to jail for stealing it. You are implying that he has committed a some real crime beyond incompetence?
I'm sure there are some AG's and Prosecutors frothing at the mouth right now to get there hands on Mr. Karpeles.
Edit: Even if the judicial system doesn't get MK... his life is probably ruined at this point if he cannot recover the funds - either because of reputation or personal safety. Bitcoin is the Wild West and there seem to quite a few shady and nefarious actors within the community.
Their cover up is what will bring legal repercussions.
"Karpeles replied that the matter is “confidential,” adding that the company had discussed its business model with Japanese authorities “to ensure that we are operating within the law here.”"