I'm guessing that Clinton will win in Puerto Rico this weekend, but Obama will probably take Montana and South Dakota next Tuesday. Just making some blind guesses about the percentages using Slate's delegate calculator, I see Obama picking up around 35 delegates between these three contests. As of today, he's only 45 short of a majority. This may be over soon.
I recognize, of course, that this math may change later this week, depending on how the Democratic Party's Rules and Bylaws Committee rules on Michigan and Florida. But it still seems like the end is in sight.