Let's see... this means that if the Christmas attack was foiled, they probably are scrambling to implement a Plan B very soon. IOW they don't feel they have the luxury of waiting for the alert to blow over so they can carefully plan the next attack.
Which would mean they don't have time for a courier to make the rounds in person (away from our prying eyes) to arrange other means of communication which haven't been tapped by the intel agencies yet. Which means they have to plan the next attack on the same compromised channels. So if we're lucky (and if the French don't screw up again), they could yet get smoked out before they get their second chance.
Looking at it from the opposite direction: If they do decide to call it off now, there's no reason to go after Musharraf right away.
OK, I've got it: Musharraf's safety will warn of Son of 9/11. If they try to assassinate him a third time, that means that Son of 9/11 is still imminent. (It's much easier to set up another suicide bombing against a convoy in Pakistan than to crash an airliner in the US.)
But if we don't hear of any more attempts on Musharraf's life for a while, then we can assume that Son of 9/11 has been postponed.