Actually there was a referendum on the future of the Soviet Union in 1991. The question was whether people want to preserve Soviet Union (a slightly improved version) or not.
The answer was "Yes" - from 70% up to 96% of people in 9 republicks voted for preserving USSR. The highest results were in Asian republicks.
Detailed results:
Soviet Union referendum, 1991 - Wikipedia, the free encyclopedia

The people's will was ignored which violated Soviet (and probably any other) Constitution.