I guess it's now mostly just about staying safe until they hit the final line, but with the TT I suppose that to an extent, they can just open up and hammer it, so long as they don't use up so much energy that they haven't got anything left for the last day. Indeed, they can't take it too easy, or they could loose time to someone, that could be useful if something went wrong on the final run into Paris.
You can make lots of what-if's about whether Froome could have gone into Yellow, or for that matter whether someone else would have done if Froome wasn't helping Wiggins, but you really don't know what impact additional pressure would have on people. As it is, the chances are that Sky is going to get 1st and 2nd place on the podium for the GC, which is pretty damned spectacular.
Thomas Voeckler completely dominated the King of the Mountains today, somewhat impressively, making sure that Kessiakoff had no chance of gaining any more points than he couldn't stop him from getting. That was pretty spectacular as well.