Iran, the Middle East, and the world at large is at a crossroads. The worst thing that can happen is for the United States to leave the Islamic regime in power in Iran. Iran is a key member of the China, Russia, North Korea, Iran quad who aim to counterbalance the United States.
Here's a few things that will happen if the regime is left in power:
1. The regime will crack down hard on dissenters. Tens of thousands of Iranians suspected of opposing the regime will be executed or imprisoned. Not a single possibility for dissent will be allowed. The Iranian regime's prestige will rise amongst its admirers - it has survived the combined onslaught of the two "Satans".
2. Russia and China will re-arm Iran to make it even more costly for the US and Iran to try again. Iran may even host a Chinese naval base along its coastline.
3. The Gulf Arab states will have their worst fears confirmed, that the US is a fickle power that cannot be relied on for the long fight.
4. Iran will pursue a nuclear arms program with even more decisiveness. They may conduct the research in North Korea to keep away from Israel's long hand.
5. Iran will increase funding and intensity of activities for terrorist activities that produce social divisiveness in Western countries.
Despite the immense negative consequences of leaving the regime in power, there are strong forces that hinder the US from dismantling the regime:
1. Russia and China will discreetly assist Iran in resisting the US / Israeli efforts. While they will not directly intervene with their own military, anything they can do, especially deniable things, to make the situation more difficult and costly for the US, they will do so. The conflict provides a good opportunity to observe how the US plans and executes its fights, a good opportunity to test their own systems against the US, using Iranians as proxy.
2. Opposition from the Democratic party, the left, and all Iran-funded lobbies.
3. The US desire to not put boots on the ground in Iran, to avoid casualties. Iran will let in militants from Iraq and Afghanistan to fight the Americans and inflict much damage.
4. Israeli will likely not put any boots on the ground for fear of an IDF soldier being captured by the regime.
An unconditional surrender by the regime, with the regime left in power in Iran will have the same effect as just leaving the regime in power.
An open-ended continuous striking of Iranian targets over the years will not work. The next US president may be not be inclined to continue it. The longer the conflict goes on, the more opportunity for Russia and China to supply Iran with intel and weapons to inflict cost to the US and Israel.
There is no choice but to remove the regime as quickly as possible, and to put in the forces required to prevent it from regaining power.