When the USSR split up, Russia agreed, with the other constituent countries of the Union, to be responsible for ALL of the USSR’s debt. Russia also agreed to accept responsibility for ALL of the USSR’s nuclear weapons. Soviet Union nukes in Kazakhstan were either dismantled or sent back to Russia. Russia also agreed, with Ukraine, to share the Black Sea Fleet. A few ships of the Navy of the USSR were transferred to Ukraine. If some Russian sailors weren’t happy about being on a ship that was now flying a Ukrainian flag, they were simply transferred to a ship flying the Russian flag (and vice versa).
In exchange for Russia being reasonable, the other countries of the Union agreed that Russia should be the SUCCESSOR STATE; they would raise no objection to Russia getting the USSR seat on the Security Council of the United Nations.
There will be negotiations between Scotland and England over the process and the terms of Scottish independence. But the question is - would Boris Johnson be as reasonable as Boris Yeltsin?