Well, if the GC is still wide open, the points competition looks to have only two possible outcomes: Cav or 'Purito' Rodriguez.
There are five stages remaining. The competition starts to favour Cav if he can survive the mountains, provided that:
1. Cav takes the sprint on Stage 18. He would have 135 points, even without any of the intermediate points. For Purito to overhaul this total, and assuming he gets nowhere in the sprint he'd need 52 points, which means finishing an average of 4th on every remaining stages inclduing the TT. If Cav got any of the intermediates this would be more difficult still.
OR
2. Cav comes 2nd or 3rd in that sprint. Purito would need over 40 points, which would mean finishing in 4th or 5th place on every stage. This would be made easier if hepicked up a few intermediate points. Still difficult though.
However, two scenarios favour Purito:
1. If he were to put in a real champion's performance and win one of the remaining stages or even get on the podium, he might have more of a chance, only needing to finish 9th or 10th on the four remaining stages;
2. If Cav crashes or misses a move on Stage 18 and gets nothing (or very few points), then Purito would only need to finish an average of 10th or 11th on every stage, and this could easily be made up for by a high placed finish or two in the mountains - he wouldn't even need to get on the podium in any stages to win the Rosso and wouldn't have to care about the TT.
However, if he's doing this well, he would be more likely to be concerned with the GC than the points... it is interesting that in the last three Giro's, the points competition has been won by a climber / GC contender, not a sprinter. I know this Giro is slightly less evil than the last couple of years, but it would still be a significant achievement for Cav to win this particular points jersey.