Though I am a [non airline] pilot, my only experience with doing CPR has been in my capacity as a volunteer firefighter for 27 years. I've had to start solo CPR four times. I did not ever make a save. However, a number of my fellow firefighters did, so I know it could be done. The most memorable thing I was told over the many years of recurrent CPR training was: "If you, as a trained CPR provider, have decided to initiate CPR, you have determined that the patient lacks vital signed - they are dead. You cannot make that worse by beginning CPR.". That was reassuring, as I know I have broken ribs.
Only once, was CPR not terribly stressful. A wife knew it had been time, when I arrived. Otherwise, there is incredible stress, and someone screaming. Worse yet will be two conflicting family members, one screaming "save him!!!", the other saying that there is a Don Not Resuscitate order, but they don't have it with them. Then you're starting CPR with two people screaming at you for totally different reasons.
In summary, starting CPR is the final courtesy one person offers to another who has passed away. If you save them, it wasn't the final courtesy, but instead and awesome courtesy - either is good.
A jet airliner in cruise flight cannot be suddenly pointed down to the nearest regional airport, for a number of reasons, which, for the first part of the flight probably includes landing weight. Pilots much more conversant with that than I will be along shortly with more wisdom on those factors.
By the way... Good Job! Thank You!