I would expect the investigators to pursue all avenues to recover the data that are readily available. My concern is that they chose to apply for a court order to compel Apple to break an encryption technology that they(Apple) have previously stated was unbreakable, in essence to destroy or diminish the perceived value of one of their products. If they are successful in cracking the encryption, then it loses much of it's value in the marketplace, as well as casting doubts on their original claims of security, possibly opening them up to litigation from previous customers. The smart thing for them to do would be to fail, regardless of the possible value of the information on the phone.