You've got to remember in a climb like that that if Sky starts Cavendish at the front, he needs to lose the length of the entire lead group to get dropped, so if it's 10% for 200 meters and he's 20% slower than the guys at the front, he loses only 40 meters. That's still comfortably within the draft once it levels out. And if the rest averages 4-5% they go so fast drafting is still a big benefit. So a break may pop off the back but unless Cavendish starts at the back of the pack he's very unlikely to be dropped.
Oh Saxocrash.
Just when I was trying to suggest a new format for those killing sprint stages.
Max 10 km. Bunch start. At minimum 50 corners. Grand prix to the winner