Remember the movie "Crimson Tide"?
USS Alabama, a U.S. Navy submarine, is dispatched on patrol with orders to launch a pre-emptive nuclear strike if Radchenko (a Russian ultra-nationalist rebel, take control of a nuclear missile installation) fuels his missiles.
Alabama receives an Emergency Action Message ordering a missile launch against the Russian base. As Alabama prepares to fire, a second radio message is detected before a rebel Russian Akula-class submarine attacks, damaging the boat’s radio and leaving the message incomplete.
With the last confirmed order being to launch, Ramsey decides to proceed.
Iran may be in a similar position, where the field units will continue to follow the last command and control orders, until new orders tell them to stop. And with their command and control obliterated, there may be no way to tell them to stop.