Large scale troops in the country will be a bad idea. Small SOF teams dealing with high value targets is doable. The Iranian military is not really the target, but the IRGC certainly is. There is a government in waiting and it's very likely the Army will swear allegiance to a new government. The population is fairly educated and can recover quickly. There is already a form of voting in the country. It's just that you are currently only allowed to vote for "approved candidates". The Shah has said the plan is to run a referendum on what form of government the people want. Likely a Constitutional Monarchy, but if they choose a republic, then he will respect that as well. He has a leadership team in waiting and clearly a lot of support in and outside the country. So the framework for voting is there and so is a ready made and acceptable transitionary governance body.
My guess is there will need to be a "Truth and reconciliation process" and a way to vet and rehabilitate junior members of the IRGC and other supporters of the Islamic regime. If the regime collapses, I see the Army coming out publicly to support the Shah's return, most of the clerics and heads of the IRGC flee. The rest are rounded up and imprisoned. Bureaucrats are ordered back to work and the new government arrives.
There will be some chaos as many of the major businesses are owned and controlled by the IRGC. I suspect most of those will be taken over by the State for a period and then sold off. Water and reliable power will be major issues as well. But the Persians are an energetic lot and free of the Islamic regime and with sanctions lifting, the country will be getting back on it's feet quickly.
There will be a low level insurgency from Islamic regime supporters and also from Baloch independence types, the former will need to be crushed and the latter can be muted with some promise of more self determination within the Iranian governance framework. The same can work for the Kurds in the North. My guess is the MEK will still be outlawed, but with a pathway for junior members to forsake that organization.