You may need to expand on what this idea of "nonterritorial warlordism" is. For all but a few, a nomadic life is basically certain death. And most warlords will lack the resources to do much travel in any case. If you mean it in the sense that there are squatter bandits, then sure. They are the unstable part of 2000. Most of them will be gone soon. Either dead or they went legitimate in the service of a higher power.People mean lots of different things by feudalism. I used to be a medieval historian and went to college and grad school at a time when feudalism was under attack as an unhelpful construct. The reason that feudalism is inapplicable to the post-Twilight War situation in my view is that feudalism concerns land tenure. Lords grants land to the vassals who in return perform military and other service. In the classical conception, this basic system of "I let you live on my land, so you work for me" goes from the king down to peasants. Despite the mentions of the cantonment system, I can't see land tenure as being all that important in the post-Twilight War world and certainly not formalized to that extent. Fundamentally, no one is that settled! Also, relations within the military aristocracy wouldn't embodied in land at all. Why soldiers follow other soldiers in this setting may be complex, but I think in approximately zero cases does it involve something like "Johnson follows Smith's orders because Smith granted Johnson the fief of Farmville." (Why anybody can order anybody else around in this setting when they both have guns is an interesting question.)
So I think what you really have is nonterritorial warlordism. It could mimic aspects of feudalism after a few decades if the cantonments stabilize. They would not be stable in 2000.
Which is also the answer to your other question. All over the world there are people with guns who listen to other people with guns. Social fabric didn't vanish overnight when the war came. In fact, more likely, it became tighter and more important. So there's plenty of really good reasons you don't just have a shootout with the guy trying to boss you around, first one being that you might not win. Close behind that is that people tend to have friends. Friends and alliances are what keep people alive, and the bandits hiding in the woods will rapidly run out of those. The same reason you don't go gunning for Tony Two-Toes because he took 10% of your profit is the same reason Lt. Smith isn't going to just shoot Col. Rogers in the face.
In this world social currency will be based on who can provide food, and in many cases that means there will be a very strong overlap with who is well-armed enough to secure the fields and workers. So governance in general will probably have a much heavier military/paramilitary presence to it than any division of power we know now, but there's still a lot of power to be derived from the social norms, titles, and structures that existed in 1995.