The Supreme Court Doesn't Need 9 Justices. It Needs 27

Most importantly though, with the absence of Brennan and his persuasiveness, John Paul Stevens might have remained moderate enough to be listed among the court's conservatives.
Of course if that also kept Charles Whitaker from having his nervous breakdown, then Nixon, not Kennedy, would have chosen his replacement. That might have gone to Powell or Carswell, but no scenario in this line of developments puts Blackmun on the court.