Tough one. Be interesting to see how revolutionary Iran would hash out without Soviet tanks rolling through Tehran. My guess is messy, ugly and altogether worked out of its system within a decade into something more stable.
Considering what happened to Iran post-war, I have a feeling that it would basically be OTL's fundamentalist regime only lacking the devastation brought on by the Soviet Invasion and with a surviving Ayatollah Khomeini at the helm. Certainly much more dangerous than today's rogue state.
On the other hand, without a common enemy in the form of the Soviet invaders/occupiers, there would be very little to unite the then fractured Iranian populace, so perhaps there is indeed a chance of Khomeini's Islamic Republic falling apart (especially with the Tudeh communists and the pro-Shah people still running about).