It would be too complicated to predict. There is a lot of things that can happen during different phases. If the US regime starts a war with Iran then Iran will start retaliating hard...
We’ve already seen Iran’s "harsh response" during the conflict with Israel—it wasn't much. This regime is only tough when it comes to cracking down on its own people. If the people get their hands on weapons in the chaos of war, it won't be a war against the US or Israel; it will be a full-scale civil war.
The US sponsored terrorists such as al-Qaeda and Komoleh are not "Iranian people", these are categorized as US regime's army since they receive funding and training from US military and under supervision of the US army.
The devastation in Israel and the losses US regime sustained are clear and the satellite imagery that are slowly coming out despite the heavy censorship is proving how Iran easily crushed the US regime and its terrorist groups like Israel back in June which we already knew considering how they started the war and then they begged for ceasefire.
And that was not a full-scale war, it is categorized as fire exchange. In case of full scale war, Iran will show these regimes no mercy and for example not a single US naval unit would remain afloat or operational.
Recently the US regime's highest military official which is the Chairman of the Joint Chiefs of Staff confessed to this proving once again how fragile and weak the US military is in case of a face off with Iran.
Knowing this, is the exact reason why the US regime has been using its terrorist proxies against Iranian people and then refers to them in its propaganda mouthpieces as "the Iranian people" and whenever the actual Iranians people crush the US Army (takfiri terrorists) they refer to it as "crackdown on people" which won't change anything. These are US sponsored terrorists and US military will be crushed if they attack Iran

Over the past couple of years we have also seen how pathetically weak the US military is too. For example in their Navy we are seeing how the suicide rates is on the rise again and the losses are amassing in their face offs with smaller and much weaker countries such as Yemen where the US military lost dozens of military aircrafts including 3 F-18 superhornets and multiple warships were severely hit that they are still going through repairs and may never become operational again.