I don't think this future will happen, primarily because I believe that there are other forces at work in the world besides political forces. But could it happen? As scenarios go, this one certainly passes any initial sniff-tests that one might wish to apply.
It could happen.
The answer to a scenario is another scenario. Simmons wants to warn us about dangers he sees as imminent. On this site, we have dedicated a good deal of time and verbiage to spinning out scenarios that speak to a very different kind of future, mapped against what we see as a relentless spiral of improvement. However, we have to concede that there are risks and choices to be made even if these scenarios turn out to be correct.
Ultimately, the future comes down to what choices lay before us, all of us -- the items that occupy our possibility space -- and the actions that we take to bring them about. Simmons' nightmare future is out there. A series of bad choices might just land us there. (Simmons asserts that most of the choices have already been made.) But that future is one of many, and I don't believe -- as the time-traveler from Simmons' story asserts -- that time is a river whose course can't be changed.
We are the river; the choices that we make and don't make. I'm pretty sure Dan Simmons must believe that, too, or why bother writing about any future?