In June 1991 there was no reason to believe the USSR wouldn't last for decades.... and by the end of the year it was gone.
I'd argue otherwise, as an amateur Sovietologist. The signs were already there in the late 80's when the Baltics started to do their own thing without any real response from Moscow, and Yeltsin's victory in the March 1990 elections was a clear sign that things were extremely unstable. Gorbachev had lost control - he tried everything to stop Yeltsin from becoming the de facto President of Russia then, but they ignored him. He'd already spent the late 80's attacking Gorbachev and demanding reforms, and he was popular with the Russian people, but not in other republics. From what I remember, this was the start of open feuding between the Soviet power structures and the Russian ones too.
Once Yeltsin won the election for the Presidency of the Russian SFSR in June 1991, it was just a matter of time. He clearly wanted control over Russia, and I suspect he would have embraced Serb-style nationalism if the Soviet leadership didn't eat themselves first.
Maybe a better example would be Czechoslovakia? They were squabbling and not cooperating well, but most observers at the beginning of 1992 would have seen confederation as the way out, not divorce.
From my point of view, it's pretty obvious now that the richer members have had enough of funnelling money into the poorer ones, only to get abused in return for it (Poland, Hungary...). I suspect that they will get their way, and funding will be tied to politics - effectively do as they say, or get nothing. While people like Ironside will proclaim "let's walk away" - the truth is that for PiS, the CAP is of absolutely vital importance. Even one year without payments would devastate Polish farming, especially as many of them rely on low-value produce.