Reddit reviews The Bear Went Over the Mountain: Soviet Combat Tactics in Afghanistan

Over the intervening years, there would have been substantially more dead young Soviet men. That sort of warfare is difficult enough in a best case scenario when you have plenty of spare parts and the authority to change tactics because you're the one on the ground and you know what's going on there.

Those men and their commanders had neither, and they were at the end of a pretty miserable supply line as well. In order for Russia or the USSR to have won that war, I would submit that significant political changes would have been necessary. Those changes would have removed altogether the entire reason for being in the war (politics and pride).

A much earlier fall of the Soviet Union might have created the political conditions necessary to win the war, but at what cost? The Soviet economy of the time wasn't quite ripe for pillaging yet. Without the level of pillaging and profit-taking seen in the aftermath of the fall in OTL, the rise of people like Putin is potentially in doubt. Certainly, the ascent of someone like that would have taken rather longer.

For Russia to have a strong ruler arising from that class, a solid military, the necessary politics, and the resources and desire for a war like that, we could move the fall of the USSR back to 1959, two decades prior to the war. Doing so would be quite likely to lead to nuclear war, making the entire question moot. A "democratic" Russia ruled by a Yeltsin analogue followed by a Putin analogue in the same relative amount of time starting in 1959 would not have ended well for the world, I think.

I can imagine a few variations that might make it possible, but precious few of them lead to a world I'd want to live in.

For background, I'd suggest two sources, both of which are reasonably accessible. Grau's collection of experiences as told by Soviets is available in free PDF from a .mil source if you search it. The Wilson Center maintains translated minutes of Politburo meetings which shed light on how the war was handled (or not handled, as it were) at a high level of the Soviet government.

But to answer your question... Several years ago I drafted a rather lengthy alternate history to that effect. It's since been lost in its entirety, but the general gist was this: A strong foothold in Afghan cities would have allowed the Soviets to pay less attention to the mountains and countryside, for there lay only despair. If and only if, the Soviets had taken an iron grip on the cities, they would then have had rather interesting paths into a few key places. Namely, Iran as a whole and possibly China. Ignoring the geopolitical implications of taking Chinese territory in the early eighties, and also ignoring the fact that the Soviets didn't want Chinese territory, it was a possibility. Islamabad would not have been a terribly difficult target to drive tanks through in those days, probably, and the natives might not have harassed a Soviet force "just passing through" the way the Afghans fought the Soviets. Iran not only has oil, but also was in a much better position than the Russians to exploit and sell the same at the time. If the Soviets had taken the important parts of Afghanistan, and carried on into Iran, that oil production could well have supported them long enough to get to an era where some of the resources in Afghanistan would make it worth slowly bringing the villages into line to exploit those resources. The actual process of drilling and mining is arguably easier (certainly different) in Iran and Afghanistan than in, say, Siberia.

Two major changes would come out of those. First, we'd likely have a USSR-US balance of power to this day, and that is not a bad thing at all for world stability so long as both sides elect relatively sensible men to lead. It gives pause to smaller states with larger aspirations, at least, which is worthwhile for stability in and of itself. When smaller states are aligned with one of two or three significant powers, no one really wants to go to war. We'd have fewer rogue states, certainly.

Further, I'd argue that inclusion of Iran, Afghanistan, and possibly the relevant parts of Pakistan into the Soviet fold would play a significant role in preventing the growth of both state-sponsored and ideologically encouraged terrorism. Had the Soviets won the war in Afghan cities and in surrounding nations rich with resources, AQ and their ilk might have been reduced to nothing but mountain bandits fighting against the Soviets. Without the extended reach of pseudo-ideological terror, it's entirely possible that the remainder of the Middle East would have sorted themselves out and undone the damage done after WWI, through a series of small skirmishes and resulting treaties. Perhaps only a few miles of border at a time could be drawn that way, but they could be drawn in a way that made nations and states make sense. Encouraging that would have gone a very long way towards softening the underlying strife in the region today.

TL;dr - Had the Soviets focused on their doctrine instead of their politics, and been ravenously more expansionist than they already were, a large part of the world might today be more peaceful.