Had MtGox been a Ripple gateway, it would still have failed all the same, except that until it did, its debt would have remained liquid and cryptographically provable. Liquidity of debt allows risk avert holders to sell the troubled asset at a discount to interested parties having different withdrawal options, willing to bet on a recovery or planning to take the legal route to recover the funds. Cryptographic provability of the balance guarantees that the exchange cannot cook his books and claim that he owes less than he really does.