I understand the point you are making about the USSR Constitutional ability to secede and that the coup showed that Gorbachev was weakened politically, but you have to consider Yeltsin in the equation. Frankly, I can't remember every detail of that period so can't say which led to the end of the USSR more Gorbachev's weakness or Yeltsin's charisma/strength. I have the feeling that Yeltsin was more of a Russian nationalist and therefore was more in favor of letting the other Republics leave the house. However, as much as there was a Constitutional tool for secession the foreign politics were in a state that allowed the Republics to stay independent. If the foreign politics and if world affairs had be different some of the Republics might have stayed. I think this is especially true of the central asian republics and Armenia, Azerbaijan, and Georgia. For example if Iran had tried to imply that they might want to join their Azeri state with the former Soviet Republic of Azerbaijan independence might not have been the future for that Republic, and it could have effected the Republics around it as well. I also seem to remember Belorussia wanted to stay with the USSR initially.