I now regret clouding this topic with the CC tangent, as I think most FTers are capable getting from loyalty schemes without resorting to trading on the internet. What's more, if anyone I knew was contemplating a one off transpac on CZ, I'd help them create a redemption list of people in our circles that have a frequent need for intra-China tickets.

Back on topic, I have a hard time valuing less than 20k DL miles at even a penny a piece (because you need DL Amex in order to "pay with miles"), but will do so here for the sake of comparison.

Assumptions:
-OP's friend flies on one of the 100% earning fares
-has no interest in flying DL or CZ again in the foreseeable future

DL Scenario:
-14,463 miles = $145

CZ Scenario:
-23,276 km
-CAN-TSN x2 (I'll use 30% discount fare because IME it's usually possible to squeeze award inventory at 7折 and below) = Y2380 = $350
-while I may be guilty of using the longest flight I could think of inside 1800 km, I'm ignoring the fact that one of the two tickets can be in business class (business class isn't necessarily more valuable than economy IMO, but it's often possible to snag business class award inventory on planes that are full fare in the back, which gives the extra miles a bit of a silver bullet quality).

One more note to the OP, if your friend ends up crediting to CZ, you should advise him that the miles have a (bit more than) 2 year shelf life, which can't be extended.