I don't really see how a successful August Coup would change much. It was already too late to recover for the USSR by then, in my estimation. The Warsaw Pact had crumbled, the Baltic States had already declared independence, Russia itself under Yeltsin was fighting the War of Laws against official USSR doctrine, and the military buildups during the 1980s Arms Races had severely crippled the economy. Even if the Communists held onto power at that point, I don't think it'd last them too much longer... beyond which, the Coup proper succeeding would take some work.
Now, if you were to go back a bit earlier to say, 1970, knock off Gorbachev somehow then fastforward to 1983 - 1985, have a hardliner follow Chernenko... then things could be interesting, considering that was the
true height of the Cold War. It's not outside the realm of possibility that with Star Wars Reagan at the helm the diehards in the Soviet party might realize that if they wanted to "win" their window was fast receeding. There are actually already
some thoughts on the matter. It's not entirely impossible that in an age of MIRV'd warheads, a last-ditch conventional war would be tried: if from the outset you only use conventional forces, your opponent is obliged to retaliate in kind as if he uses nuclear weapons first MAD comes into play. Unfortunately, once one side starts to lose, they're liable to use them anyway... and Soviet doctrine tended to include heavy tactical use of NBC weapons.
I guess I could work on such a thing, though it's my estimation it'd either end in nuclear holocaust or with an initial Soviet advance before American assets began entering Europe in force. Given the performance in Gulf War I but little more than half a decade later, I am inclined to say Allied technology would probably match or beat Soviet numbers. If it didn't end in nuclear annihilation, it'd probably be a semi-draw brought about by internal dissent in the Soviet Union, particularly if Gorbachev
was around but had chosen to go this route, with the likely collapse of the Soviet Union thereafter...
Alternatively, a hardliner could replace Gorby and not act, and Communism might continue on, though given its stagnating nature in the 80's and the inevitability of reform, I can't imagine it lingering on all that much farther really; cracks would appear sometime.