Its in a Soldier's mentality to defend his nation when it is at war, no matter what so for the beginning of the conflict there wouldn't have been mutinies, there would have been revolutions maybe, but they would be put down pretty quickly
That's what people like to think, but it happened a thousand times in history that soldiers refused to fight with the enemy at their doorstep. It isn't exactly that defeat would end in the total destruction of the nations and its people. Sure, the people were fed scaring images, but not total extermination. We would see people giving their lives for the system they believe, and we would see mass surrenders and desertion by those who didn't.
My personal opinion: Had the Warsaw-pact gone to war, it would have crumbled under its own weight. There were too many disgruntled people already who multiple times had open conflict with the government, and then they would be asked to support a war-driven economy? They would be asked to give their full support and their lives for the system that took and was taking away their family and friends. You are overestimating the communist system. It doesn't work, especially not under war. The fact the USSR even got to live trough WWII was due to Hitlers incompetence and American dollars.