How about when TWO candidates have zero probability of amassing the delegates necessary to win the nomination?
NEITHER can get the necessary votes. There is no rule saying go with a plurality of delegates. If anything it should, and I think will, go to the popular vote. That's where it gets messy because while we obviously can't count delegates for FL and MI, a good argument can be made for counting the popular vote for FL. MI is difficult but I would give the 40% "Other" votes to Obama and give Clinton the 60% of the vote she won. Again I'm talking about the POPULAR VOTE, not delegates.
Obama could have ended this months ago. He's not a finisher.