The US are incapable of finishing the job. That's what they tried to do in Iraq and look how it turned out. Iran is much more organised, has a competent secret police, is huge and better armed than Iraq was. It's physically impossible to carpet bomb the country like Israel is trying to do to Lebanon, so whatever you do you can be sure that there will be plenty of armed partisans. If the central power disintegrates, there will be a mess of Kurdish forces, the remains of governmental armies, and you can expect other interesting groups to show up along the borders with Iraq and Afghanistan. Even if the US were lead by competent people with a decent strategy it would be worse than a long shot. And they are not.

They are also incapable of forming a coalition. They pushed the Saudis and all the Gulf states, who hate Iran with a passion to the moderate "maybe starting a war was not such a good idea" camp. The latest noises about forcing them to make friends with Israel is exactly what you would do if you wanted to be absolutely sure that they will never help you. The noises about annexing Greenland and Canada made sure that nobody in Europe is going to be part of any coalition there willingly.

That's what happens when you take stupid decisions on your own because you're a big bully boy and allies are for chumps.

Destroying what remains of their missiles and drones and forcibly reopening the straits is absolutely possible. Estimates vary, but so far about 50% of their offensive capabilities seem to have been destroyed. Continue combat operations and destroy the rest. Escort ships trapped in the Gulf out. Maintain the blockade on Iranian ports to apply maximum economic pressure on the theocracy. I don't care about the internal politics of Iran. If the country descends into chaos or civil war, so be it. Hopefully, this may result in a collapse of the so called Islamic Republic. It is for the Iranians to decide what government they want, so long as it does not interfere with global and in particular U.S. interests.