The US will claim "victory" and pull out without effecting regime change, in the expectation that the Iranian people will "rise up" and overthrow whatever version of the regime remains in power. This will lead to an internal power struggle and substantial further deaths, and Iranian proxies seeking revenge against US and other western targets, whilst we either get a collapsing failed state, as with Iraq, Libya, and Afghanistan, or a successor generation of the same complexion as the one Trump and Bibi have been culling.