It's very tough to see how Cavendish will pick up any more points.
The first climb tomorrow is relatively manageable, but either there will be a break already or people will attack on the climb. If Sky ride fast enough on the climb to bring the break or attackers back before the first sprint just 10km later, they will presumably drop Cavendish.
About the best option I can see for him is to try to get into the break, just as far as the first sprint point and then knock it off. I can't see Katusha chasing hard because they have bigger fish to fry.
Even still though, it seems like a pretty tenuous hope. At least some of the people going in breaks over the next couple of days will be very good climbers, given the profiles, and they will want to keep a strong pace over the first climb to build their lead. Whether he's in a break or in a peloton which is actually trying to chase down a break it would be very tough for him to stick the pace up any real climb.
It's more likely that a break takes points from Purito than that Cavendish gains more himself.