In the extremely unlikely event that all $120 billion was drained from cold storage all at once, I can only speculate on what would occur. They might not be completely ruined but it would destroy their reputation and credibility. They still have a lot of altcoins and fiat, which could cover some of the losses but it would take a long time to fully restore customers’ balances.
Gox was a HUGE disaster and it is no where close to the monster Markets and their Reputation or Business will have to confront in case of such a significant drain. It would destroy Coinbase forever, there is no way so many people would be stupid enough to continue allowing them to handle their Money after one such catastrophe.