Even though resuscitation efforts were not enough to bring Michael Jackson back to life, there has been many rescue nurses who have been able to resuscitate and stabilize people before they get to the hospital, enough to prevent death. People have also been resuscitated in hospitals in the emergency room, in the middle of surgeries, or when something goes wrong in the recuperation room. Many resuscitating attempts have been successful, but tragedies do happen. Depending on how sick or how much danger is the person in, some people can't be resuscitated.
Resuscitation efforts do not normally last any more than 10–15 minutes, by the time that much time has passed, resuscitation efforts are abandoned as it is usually too late to attempt resuscitation (after 15 minutes or so).