On the original point raised to create the thread, I do not see much similarity beyond supply of airpower by a foreign power and the presence of foreign nationals volunteering as individuals to fight alongside the Taliban.
The Spanish Civil War was seen largely as being just that and was fairly well polarised. At the time no international threat was perceived from the outcome. Germany, Italy and Russia used it to find out how well their new toys worked to the detriment of the Spanish people as a whole.
My comparison to Afghanistan at present is with the state of the Anglo-Scottish Border during the reigns of Elizabeth I, Mary Queen of Scots and James VI. There is a very good book on the subject entitled "The Steel Bonnet" by George MacDonald Fraser. The area lived on an near permanent war footing for almost 350 years. The structure was such that the various families had no other loyalty except to family. Alliances, truces and feuds respected no boundary imposed by nationality and at times were downright bizarre in terms of rationality and make-up. In Afghanistan you have tribal leaders and warlords leading their respective tribes and ethnic groups into and out of alliances and pledges of loyalty to suit what ever happens to be the flavour of the day. Should the Taliban head for the hills to mount a guerilla style war it would be very difficult to predict how all these factions would react at any particular time, or circumstance. In my parallel from history, the solution came when James IV of Scotland became James I of England. The pacification of the Borders was brutal and measures against offending "riding families" were ruthlessly pursued. The instruments of law and order on both sides of the border were the appointed Wardens of the March,who on analyses were no better than the brigands they were prosecuting. It did give the population in general some respite and the area began to enjoy some measure of prosperity - it took a long time on the borders and it will in Afghanistan.
As to whether the Red Army would have rolled all over Europe had Stalin continued the war, I think not. They would have been extending their lines of communication through increasilngly hostile territory, their airforce was entirely tactical and their forces had never been subject to strategic bombing. American and British fighter aircraft were superior and the first jets were about to come into front-line service. Russian command and control of their armour and air-power was only marginally better in 1945 than it had been in 1941. An example, when Guderian was re-instated as a commander on the eastern front late in 1944 using effective command and control of extremely limited resources, it required the attention of two Russian armies to counter the defence offered by two German Divisions.
Fortunately, as a last resort, America had the bomb and good old Joe Stalin didn't.