CanadianGoose
Banned
I thought about your questions over a weekend and I realised that, although I've read many Russian post-apocalyptic stories about the world you envision, none of them had plausible descriptions of PODs worth talking about. Usually they just say "OK, our country disintegrated and all the hell broke loose, so now we're at year X post-Event and see how miserable it is". I would say that "extreme dictatorship" POD would not work. As Northern Korea proves, you can create autarcic economy and live with it for ages. With USSR having significant sources of hard currency (otherwise known as oil, gas, ores, lumber), fear-ruled society can enjoy it's evenly spread misery for a long time.
So, most plausible POD I see is something along the lines of Gorbachev's reforms going more FUBAR than they went IOTL. Basically, you need to create food and consumer goods' shortages artificially, then have people cling to what they have, then get regions to put local supply of food and consumer goods under tight control (there were attempts IOTL to do it, with regions placing restrictions on export of certain fudstuffs outsude of it's borders) and somehow prevent regions from forming barter-based markets for their goods (money-based trade have to be dead at this point, but this is not impossible to do, people had very low opinion of rouble's buying power IOTL, one major panic is enough to start chain reaction of refusal to accept roubles as payment for purchased goods). At this point you have more or less "big city plus it's hinterland" situation, with each city-state acting virtually independently and for some mysterious reasons refusing to barter (that's the second huge problem you have, as restrictions on barter tend to ease naturally as soon as people realise that they need stuff from other areas and can get a good exchange rate for the stuff they do). But, if you somehow managed to sustain the situation like this for a couple of years, peoples would become desperate enough to actually start raiding "outsiders" en masse (basically scenario #2 from my 1st post in the thread). Isn't it the future you want?
As far as USSR's non-Russian republics are concerned, that scenario, coupled with old tribal feuds, would lead to massive societal desintegration even sooner. Look at Tajik civil war for inspiration.