Ah, but that brings up another question. Would the Soviet Union still had the motive or cause to even invade Afghanistan in the first place? And I think on Vault Wiki, it says that the US and Soviet Union had a more open relationship with one another, so if the Soviet Union did still invade Afghanistan, would the Mujahedeen still been backed by the US (via Stinger missles etc.) or would the US just looked the other way, and agreed with the Soviet Union?
This is dangerously close to present politics, but I'm going to allow it for the time being, on condition that all members refrain from any kind of rhetoric, grandstanding, or jingoism.
The reasons for the Soviet invasion of Afghanistan are complex and regional. Afghanistan has long (and often successfully) been used as a sort of passed pawn to cause trouble for perceived enemies of whoever the faction in power is allied with. The Soviet Union was long allied with Afghanistan against the British occupation, and the Afghan army was largely Soviet-trained and sympathetic to the country's large Marxist faction, the PDPA.
There were two coups in the 1970s: in 1973, King Zahir's cousin Daoud overthrew the monarchy; then in 1978, the PDPA, backed by the army and probably encouraged by the Soviets (who were worried about Daoud's incipient Western leanings), overthrew Daoud. The PDPA government was a failure: deeply divided, brutal and unpopular, lost support of the army, and faced an Islamist insurgency backed in part by the Carter administration (Operation Cyclone) as a means of creating trouble for the Soviets. The government repeatedly called for Soviet military assistance, and finally got it in the form of an 80,000-troop invasion that decapitated the PDPA.
So yes, I suppose that if Washington and the Kremlin had been interested in constructive dealings over troublesome places like Afghanistan at that time, the invasion might have been blunted, and US backing of the Islamists might not have occurred.