People in River Crossing didn't strike me as left behind. I think of them rather as of those who remained to preserve the basic values while everyone else rushed on along with the world.
Isn't staying to preserve values while everyone else rushed on along the very definition of being left behind? And don't forget, they're all going to die off. They have no young people to carry on...their younger citizens all left. Moved on without them. I think the people of River Crossing are probably my favorite people in the series. They seem so sad and so real.

Roland and his tet are hope like the threaded stock - it could be that three will be reversal because most of the inventions of the Old People cannot be used anymore.
I think I would agree with this idea. Although I'm not sure reversal is the right word. It has been long enough that things have started to heal (someone else mentioned that earlier in this thread) and the moving on has slowed. The machines can no longer meddle. And as the moving on slows, the people can start to make the new world their own and move along with it. The only question is, how many people are left (at least in mid-world itself, not including the outer arc) that are capable of that? Or even capable of recognizing it?