Yeah, tactics are in Froome's favour. If Quintana attacks Saxo will have to chase to defend their GC position well before he closes the almost 4 minutes more to Froome than Contador. I don't think it's good tactics to bluff that much.
Honestly, I think if Contador felt good on Sunday, he would have countered, but he didn't, and that's game over. Froome closing the gap on the flat to Valverde and Plaza by himself was the moment it ended. If he hadn't closed it, or if he had dragged others with him and then they attacked him one by one ala Contador Paris-Nice 09, that would have been the best chance to crack him. Valverde is realistic and doesn't expect to win. Contador is another story if he feels okay. The only thing to do is attack and hope Froome has a bad day, which is unlikely.