Almost all of those funds are held in offline storage where the risk of thefts is significantly less compared to hot wallets. I’m sure they’ve eliminated any single points of failure, so it would require multiple people colluding with each other to pull off a heist. Even with insider collusion, forensic analysis would identify the culprits. The odds are not in the favor of the thieves being able to pull it off without facing significant legal consequences.

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.