If _everyone_ temporarily withdrew their funds without a hit the day they relaunched, they would have proven their solvency. The fact that anyone who tried was able to is not proof of solvency.
I'm not sure why I am arguing this. They obviously have handled a major problem in what seems to be a good fashion. But we don't really know, do we?
If everyone withdrew cash and bitcoins, they would need to have customers funds. They should sign Bitcoin addresses and get their bank accounts audited.