There was an EMT on the flight. From what I read, it took 10 minutes to get her heart beating after he started rescue efforts.
In 10 minutes, her brain may have been severely damaged, as may have been other organs. If revived in 20 minutes, a patient may survive, but damage to the organs will start sooner and the damage could be serious and permanent.
I don't know how long my heart stopped, but I do have some residual effects. My memory and concentration are shot and my sense of balance is off. For many patients, the brain damage is severe -- persistent vegetative state. If that was the alternative for Miss Fisher,, perhaps it's a blessing she did not survive.