When you get right down to it, as a purely virtual asset the crypto isn't anyone's property. Coinbase holds some keys which give it the ability to sign transactions on the blockchain, a service which has value. They owe their depositors the service of signing such a transaction on request transferring some quantity of deposited crypto to a suitable withdrawal address; the value of this service to the customer is the market value of the crypto. However, it does not seem likely to me that this service Coinbase owes to its depositors would be prioritized over their other debts, especially if that meant selling off other property to buy crypto so they could complete the transfers.