It could have happened. And him winning the nomination is no less likely than him winning the GOP nom.
But how could it have happened and what differences would we have seen in his policy platform? Or in his style of communication.
It would have been a lot better for America. Instead of a choice between the Orange Monster and Crooked Hillary followed by a choice between the Orange Monster and Sleepy Joe, they'd just have been able to elect the latest descendant of Prescott Bush and had a competent New England Republican who pretends to be from the South.