They don’t really need to bother that much tomorrow though do they? I’m sure they’d chase down anybody within 10 minutes of the lead who gets in a break, but anybody within 10 minutes of the lead will know that and not bother.
There will be a break formed of people at least 20 minutes behind on GC. Sky will just ride tempo on the front for a while, let the lead get up to 10 or 15 minutes (depending on how close on GC anybody is) and wait to see if any of the sprinters’ teams want to chase it down. Froome won’t be the only one protected – GT and Porte won’t hit the front tomorrow either.