What's the likelyhood of a SHTF scenario? If you take the long view it's 100%. Between natural disasters and terrorism, eventually something will happen that at least temporarily leads to a major breakdown of our institutions. Could be tomorrow. Could be 900 years from tomorrow. I don't think its something any of us has the ability to predict.
But, if you think about it, in the last couple of years we've suffered some jolts i.e the Oklahoma City bomber, the blowing up of the World Trade Center, a massive power outage on the east coast. Clearly the world is a nasty place and there are many people in it who wish to do us harm. Moreover, every day we are developing increasingly deadly weapons of mass destruction.
However, to me the more interesting question is if the s*** really does hit the fan how much control we have over our own destiny. Clearly there are certain scenarios where all the preparation in the world won't make a difference. If some terrorist sets off a dirty bomb and you live 500 yards from ground zero, having a 200 gallons of drinking water, a 2 yr supply of MRE's a Les Baer "Thunder Ranch" AR15 and 5000 rounds of ammunition won't mean s****.
In fact, an argument can be made that those of us who are the best prepared merely make ourselves a more attractive target for the maurading mobs. (Lets get the guy with all the assault weapons and a 2 yr supply of food).
Finally, if our worst fears come to pass, how many of us are prepared to do what it takes to stay alive? If your neighbor insists you share your limited supply of drinking water with him are you prepard to kill him to conserve this resource and increase the likelyhood of your own survival?
I think the bottom line is that few of us have any real sense of what a true SHTF situation would look like.
Of course that's just my opinion and I could be wrong.