Did Mary Jo Kopechne survive for an extended interval breathing in an air pocket trapped in that vehicle, meaning that she could have been rescued if it were reported immediately?

This, in fact, is the case and is most unfortunate in having worsened a terrible situation to begin with. It was bad enough that the accident occurred and resulted in her death, but then to see she was left behind to die, seemingly with callous disregard or suspected callous disregard for her welfare, truly adds great torment for all involved in considering the meaning of this event, even for those outside observers only wondering about the role of Kennedy in his further undertakings and to what extent he deserved punishment for what happened, or can be forgiven, or that no forgiveness might be truly necessary. Most would pin this on him were it known at the time unequivocally and would have been his downfall. This is how humans perceive things. So we are not saying that is divine judgment and condemnation. It is simply understanding human nature and knowing what the outcome would have been, quite decisively, with a catastrophic loss of public support that would have been permanent and sidelined him effectively from any public service thereafter.