Azeri S-300 is no threat to Iran. First thing Iran will do is saturate the airspace with missiles, destroy them then proceed with hitting, targeting Nakhchivan dozens if not hundreds of cruise missile and ballistic missiles.
Simultaneously Iran will also saturate the air with a variety of drones. Karrar interceptor drones can do a great job of destroying any enemy drones before they even get close to the border.
Meanwhile Iranian drones along with missiles would wreck havoc on enemy targets. Iran might even use some fighter jets to launch cruise missiles at high value targets. This will be followed by rocket barrages, small, short range hand launch suicide drones, artillery, etc.
Under all that cover Iranian troops, including armored units, special units, sabotage teams, snipers, ATGM teams, could easily proceed into Nakhchivan through a dozen different entrance points, some on road, some off road.
Turkey only has access to Nakhchivan via one narrow, winding, mountain road in the very northern tip of Nakhchivan. It's a choke point. They would be extremely vulnerable and their convoys could easily be targeting and destroyed. Iran has an extremely potent and multi layered air defense network. Any air support for Turkish, Azeri troops would quickly be chased away.
Iran has a huge geographic advantage when it comes to Nakhchivan. Even Baku has no direct access to Nakhchivan and Turkey has no direct access to the Baku enclave. Both the Baku enclave and Nakhchivan are separated by Armenia. In between there are Russian soldiers, Armenian soldiers and soon Hopefully Iran will have some bases there. I wouldn't be surprised if Iran also has underground facilities which lead straight into the enclave already.
Anyways hopefully it won't come to a direct military conflict and diplomacy can solve the issues at hand. However if they cross the line the threaten Iran's sovereignty and territorial integrity, Iran must respond. Baku has already allowed the Israeli's to launch several drones into Iran from Azeri airspace. Next time they do such a thing Iran has to respond with overwhelming force.
Iran doens't even have to launch any offensive operation. Merely launching missiles at the source of the Israeli drones inside Baku or hitting that airport, airstrip with a few dozen missiles will teach them a harsh lesson. Again I hope that it doesn't come to this but if Iran's sovereignty and territorial integrity are violated again, Iran has no other choice. Iran has been patience enough with these arrogant roaches.
Under what pretense can Iran ban military flights to the autonomous region? Iran doesn’t control that region.
location of Azeri S-300PMU2’s