Historians do not generally like to describe events as "inevitable," because to do so denies the role of human agency, accidents, and other factors in shaping events. Many things could have happened to preserve the Soviet Union, and determining what those are depends largely on how one interprets the cause of its collapse. There was nothing inevitable, for example, about the rise to power of either Ronald Reagan or Mikhail Gorbachev, both of whose policy decisions helped to hasten the end of the USSR, inadvertently in Gorbachev's case. To cite a few Soviet policy decisions from the late 70s onward, there was nothing saying that the Soviet Union had to invade Afghanistan, look the other way at reform movements in Eastern Europe, pursue perestroika or glasnost, or increase military spending to compete with the United States. There was nothing inevitable about the secession of the Baltic states from the Soviet Union, or the USSR's decision not to crush the uprisings with military force (which they came very close to doing). Nothing was preordained about the rise of opposition leaders like Boris Yeltsin, nor the thousands of Soviet workers who struck in support of accelerated reforms, and in opposition to the economic failure of perestroika.
From an American perspective, Ronald Reagan's decision to place increased pressure on Soviet leaders through military, economic, and diplomatic means was hardly inevitable, indeed it was a departure from previous policy. None of this is to suggest that the collapse of the Soviet Union was not related to deeper structural issues with the government itself (though those defects, too, were the result of bad human decisions.) It is just to point out that human action brought about the collapse of the Soviet Union, not some "forces of history." Indeed, this is perhaps why the collapse of the USSR came as such a surprise to most people at the time.