We can only speculate on what might have allowed the Soviet Union to survive another thirty years to 2020, but the proximate causes of the fall of the Soviet Union are quite apparent:
[List=*]
[li]The oil crisis of 1979 which engendered diversified production of oil and other energy sources resulted in a decline in global oil prices which reduced hard cash coming into the Soviet Union from exports,[/li][li]The costly invasion of Afghanistan which highlighted the weaknesses of the Soviet military and increased dissent in domestic support for the political leadership,[/li][li]The explosion and resultant radiation release of Chernobyl reactor #4, which undermined international confidence in the Soviet leadership for failing to disclose the incident and the subsequent costly followup, and[/li][li]The liberalization of political control and relations with the Warsaw Pact nations, and in particular the decision to not intervene in the labor unrest in Poland (largely led by the Solidarity movement).[/li][/LIST]
The Soviet Union was always bankrupt and relied heavily on its more productive Warsaw Pact nations and outlying republics for basic perishables and manufactured goods. There is no particular reason that the Soviet Union couldn’t have continued on this path indefinitely, albeit with slowly declining productivity and increased dissent; it was not as if the population had any real say in the governance of the nation, and the Soviet intelligence apparatus was quite good at isolating and punishing political dissent. However, the younger generation of up and coming leaders in the CPSU had been exposed to Western economics and recognized the advantages of modern production and manufacturing methods even if they did not fundamentally accept the ideology behind quasi-free market economics, and the accompanying flow of Western products and entertainments to the families of Soviet politicians probably had as much or more to do with acceptance of liberalization as did the actual economics of the failing Soviet economy.
In fact, circa 1980, almost nobody predicted the collapse of the Soviet Union (except by nuclear conflict) within the foreseeable future, and even the few that did such as Aleksandr Solzhenitsyn, didn’t predict it to happen as rapidly and largely peacefully as it did. (Solzhenitsyn was one of the most optimistic prognosticators of Soviet collapse, and even he was estimating a failure around 2000.). The actual collapse happened so quickly that many analysts thought it was a ploy of some kind to divide the Western powers even though such a wide scale deception would be essentially impossible for the Soviet Union to have conducted. The reality was that Gorbechev simply underestimated the impact of the social and economic reforms that he implemented. Reagan happened to be lucky for being in the right place at the right time and being remembers for mouthing some hardline soundbites, but the collapse of the Soviet Union had far more to do with the internal politics and the Soviet economic situation coming out of the 1970s than it did with any threats posed by the US and NATO.
The way to maintain Soviet solvency, such as it was, would be to continue to impose authoritarian governance of the core Soviet republics and critical client states while avoiding costly conflicts. China continued to to this into the 1990s (and is still doing so today) and it has worked well enough for them, although they have certainly pivoted their economy to a export-oriented manufacturing economy which is trying to achieve parity with the United States, Western Europe, Japan, and South Korea in the breadth and quality of products offered. The Soviets were never prepared to do this, probably because they never experienced the failures of the Cultural Revoltion and the Great Leap Forward, but also because they had evolved to a system to prevent powerful leaders from imposing a reformist vision post-Khruschev.
A more interesting question is given the right decisions by the US and NATO powers, how quickly could they have engendered collapse or dramatic reform of the Soviet Union had they not misunderstood Soviet motivations (the protectionism of the Warsaw Pact as a buffer zone against invasion versus the assumption of expansionism, the true weaknesses of the Soviet economy and military, divisiveness within the Soviet and CPSU ranks)? The Soviets certainly built the metaphorical “Iron Curtain” using states essentially annexed after the destruction of WWII and installed puppet leaders beholden to their interests, as well as engaging in foreign insurgency aroudn the globe at levels unseen since the height of the French and British empires, but the Soviet economy had been failing for decades before WWII (arguably since its very inception) and the leadership always divided along personality camps. What would it have taken to forment the kind of liberalization that awaited the arrival of Gorbechev and his younger generation of reform-minded politicicians to initiate the necessary policy shifts that would alter the stance or result in the collapse of the Soviet Union?
Stranger