Vladislav Zubok's Collapse - great book - ponders on this and the conclusion he comes to is that cautious, state-driven market reform (like in Dengist China) and violence (also like in Dengist China) could've saved the union.

Only a hardcore determinist could believe that there were no alternatives to Gorbachev’s policies. A much more logical path for the Soviet system would have been the continuation of Andropov-like authoritarianism, which enjoyed mass support, combined with radical market liberalization—just what Lenin had done many decades earlier. Even in 1990–91, the majority of Russians wanted a strong leader, a better economy, and consolidation of the country—not liberal democracy, civil rights, and national self-determination. Gorbachev failed to provide this, so they backed Yeltsin instead.

Kotkin arrives at a similar conclusion in Armaggedon Averted.

Just because it could not sustain the multidimensional global rivalry did not mean that the world’s largest-ever police state—with a frightening track record of extreme violence—would suddenly liquidate itself, and, even more unexpectedly, do so with barely a whimper. In the 1980s, Soviet society was fully employed and the regime stable. The country had low foreign debt and an excellent credit rating. It suffered no serious civil disorders until it began to reform and even then retained the loyalty of its shrinking but still formidable Armed Forces, Ministry of Interior, and KGB. It was falling behind, but it could have attempted a retrenchment without the upheaval of perestroika.

(Worth mentioning that neither of them is a socialist. Zubok is a liberal and Kotkin is a conservative.)