Russia will bump up arms shipments to Iran. We'll have no choice but to strike interior of Russia. Russia will not hit mainland US, but will attack US bases across Western Europe. This will be WW3.
Russia needs everything it can manufacture for itself to use in Ukraine, and they have already gotten everything useful there was to get from Iran, so the latter is on their own.
This absolutely will not happen. Iran has been shipping missiles & drones TO Russia, because Russia can't domestically produce enough of either to sustain their war against Ukraine.