So what do you think will happen? how would you react Atheist?

You are not just thinking out loud. You stated, "This, I find most likely to happen." That's paranoia. No one is going to take away our Constitution and our Bill of Rights. Yes, we may be attacked again. Muslim extremists still exist. As an atheist, I will deal with it the same way I dealt with 9/11. I will grieve for the loss and support my government in their efforts to bring whoever does it to justice. What do you have in mind, Christian?