It's not entirely clear to me what the OP is asking, but the article proposes that certain types of catastrophe are practically inevitable, and proposes "transition plans" for avoiding the worst of it. This isn't so much about "sustainability" as it is "survivalism." That's an interesting topic in itself, at least different, but not what most of you have been discussing for three pages.
As for "sustainability" itself- the term has many different meanings, and one's conclusions are different depending on which meaning one is using. If by "sustainable" you mean that humanity learns to live in some sort of perpetual balance with the rest of the ecosphere, then humanity has never been sustainable in that sense, and seems to be making no progress toward such an end.
If you simply mean the survival of global human society in some form, that has always depended on opportunities for economic and demographic growth. As long as there is room to expand, we are sustainable in that sense. Since the traditional forms of economic expansion (the development of more land, the refinement of raw materials including fuels, the expansion of the available pool of laborer/consumers) seems problematic for various reasons, our continued "sustainability" depends on finding future opportunities for expansion and growth that don't kill ourselves off in the process, or allows our civilization to fall apart.
Ultimately, that means producing and consuming with much greater efficiency and less waste than we currently do. Ultimately, that will happen anyway, as resources run out, but it would certainly seem desirable to be able to change our economic infrastructure without the costs and turmoil that scenario implies.
Given that returning to an agrarian society is unrealistic, and that economic waste and inefficiency actually cant be reduced to zero without doing that, and that in it's current form our global economic process seems to be heading toward a crisis of some kind at an unknown level of severity, and that when this crisis comes we will adapt like we always do, then the question becomes how long will this transition take, how sever the crisis, and what we could do right now to extend the amount of time we have.
The development of Green Technology can (and will) continue. Some degree of "localism" seems inevitable, although how much and what form this will take isn't clear. And we need to develop a much better way of accounting for and modeling economic costs and waste than we do.
The primary barriers right now are political and cultural. People still seem more worried about avoiding having to shoulder more of the burden of transforming our economy than others do, than actually getting it done. So far, for every proposed change, some constituency claims that it treats them unfairly.
It will take time to overcome those barriers. We are making observable progress. Whether that progress will prove fast enough is anyone's guess.