you know who might have stood a plausible chance of winning? _Ted_ (who had not had Chappaquiddick) - his name was seriously floated even by Daley, but EMK was not interested that year and in later years it was too late.
if campaigning for HHH doesn't flip '68, would guess a surviving RFK would be the 1972 candidate against Nixon, lose, and then be a Senator as long as he wanted. (He might wind up going in interesting directions - he was very Catholic and I don't know what his relationship with Roe would have been.)