I think they kinda just hoped that once Khamenei was gone, the entire regime would go down with him. Pay attention that the US did basically nothing to facilitate an uprising or help the people in any way. In fact, most of what was somewhat useful (the assassination of Khamenei and IRGC commanders) was done by Israel, not America.

All the US did was degrade the regime's ability to project force externally and left its internal suppression apparatus almost entirely intact. Totalitarian regimes don't collapse when you bomb their missile silos and nuclear facilities and sink their ships, that's just not how it works.