Tehran wouldn't be enough. You are thinking Syria where some form of Anti-government forces held most of the country's land area, so when Damascus fell there was virtually nothing left for the government. The Government holds the majority of the country, and their forces haven't been hollowed out by a decade of civil war. The IRGC got its senior membership ACK'd but their rank and file are still largely intact. Likewise the regular army is still intact and as long as their leadership doesn't coup, even if the Ayatollah & friends were forced to abandon the city, they would be able hold the rest of country easily as long as no one was able to peel away official government forces.
This is why I cautioned about not looking at Syria for how things will go down. Its completely different scenario.
It will all come down to if reports of Iranian Army defections are true and the scale. If the Iranian Army en-masse decides to mutiny, then its as you describe. I don't see things going down that way country wide, and I think its more likely coordination failures see the protests falter, get repressed, and smothered.
But the most likely "good" outcome would be a syrian civil war situation where anti-government forces and defecting regular army take and hold territory. But they'll need heavy tactical air support while they use both hands to attempt to locate their asses.
Different sperg out after getting sack-tapped by the Jews