As I understand it, organs have to be transplanted within 24 hours of the donor’s death. Beyond that they are not viable
Not necessarily true, especially for brain-dead donors as opposed to cardiac-death donors. A young healthy brain-dead individual with good cardiac function maintained on a ventilator can preserve the body’s organs for days.
Obviously sooner is better, but I am not aware of any defined timeline in a case such as the one presented.
if the organs are not kept alive, they are useless. Once dead the organ is dead and cannot be brought back to life. They can be removed from a body that is still pumping blood and kept alive for a period of time, but dead organs are dead and useless.