I think the chances are pretty good.
In regards to Al Qaeda on a question I asked a while back some mentioned that the US keeps the wars going in the middle east in hopes that the terrorists will be occupied with the Americans in their backyard and be less likely to plan some big terrorist attack on US soil. That idea kind of makes me sick, but I am not saying it could not be possible.
And, it seems we ignore acts of terror in other countries even when it is done in front of our embassy. All through the Obama McCain run the Republicans kept saying that Bush kept American’s safe and there had not been any attacks since 9/11 http://www.cnn.com/2006/WORLD/meast/09/12/syria.embassy/ why doesn’t the car bomb count in 2006
Other random terrorist actions can happen at any time and there is probably little we or any government can do about it.