It's not hard to imagine the most likely scenario. At some point, Mark lost some coins. They were either stolen or lost through bad coding/accounting. He told nobody about it and thought he could either get them back or make up for the missing coins in some other way. Some attempts to recover or replace them we're partially successful and other attempts made the problem even worse. As the situation got more desperate, Mark resorted to greater and greater violations of ethical behavior until he could no longer even operate as a fractional reserve due to cash flow completely drying up.

It is very likely that the vast majority of depositors funds are gone forever, and not just the crypto. The willybot could have very plausibly been Mark buying goxBTC at ABOVE market rates just to keep the exchange operating and BTC withdrawals functioning until a miracle occurred and the lost coins were recovered, or until a new source of revenue could be found to sustain operations and keep the charade going.  Mark's failure to own up to his mistakes turned a substantial but survivable problem into a colossal life-destroying disaster for him and many of his customers. Despite this, he is STILL not owning up even though nobody but the most deluded wishful thinkers believe their is any hope of recovery. At first he didn't ask for help out of pride or embarrassment, but now he must subconsciously know that there is no way out. Denial is all he has left. In this context, his behavior makes sense. It is the only context in which his behavior makes sense.

There is no coming back for Gox. The damage is catastrophic. The point of no return happened months ago if not years.