I really enjoy the microscopic scrutiny of the US in the first few days after it starts a new round of hostilities. Always a litany of failures.
Regime removal is easy; replacement is hard. Iran did have a bit of democratic tradition decades ago, but not enough to shake revert-to-authoritarian mode when things got tough. It was certainly politically stunted by the Allied meddling in the '40s and the colonial meddling before that, but I also haven't seen evidence of any credible long-term Iranian-government-in-exile projects/think tanks, let alone one that has a well-developed plan for everything that has to happen to get from occupying the institutions to holding the first elections and initiating a project to write a new constitution. That's the greatest weakness.
There are always competing governing wannabe factions waiting for opportunity. Some are not necessarily domestic. A period of civil war is certainly on the table.
Nothing done by western countries has ever been acceptable to the extreme political left (the ones who are always out there with the signs deploring attacks against reprehensible regimes); presumably they want all non-marxist governments to fail and become some flavour of marxist. Ignore them. What does that leave? Maybe just allowing countries to repeatedly try and fail until they get to some kind of non-authoritarian government.
Iran is a special case. Repeat "Death to Israel/America" often enough and work obviously and credibly at developing nuclear weapons and delivery capabilities, and Israel and America are not bound to ignore the threat indefinitely.