This is one of the first of this type of story where I found the events to be believable and probably close to what will happen in the event that we lose the power grid and gas supplies. Now, I think the chances of some group being able to coordinate both is a little stretch, but I believe that if anything is going to happen in the future, it will be the loss of power.
I can totally see society breaking down that quickly with no power and communications going out in our tech heavy world. I prep a little myself, but I have no idea how I could defend my stuff whilst living in a wooden house surrounded by thousands of others.
A good book to get you thinking about what you would do if all this happened.