Major flaw with this argument. This is pretty much what we tried to do in Vietnam- Not take out the Hanoi regime, but just have the "limited" goal of propping up a regime in Saigon. We took 56,000 casualties, spent 8 years of heavy fighting, and at the end of the day, the Saigon regime folded like a cheap shirt when we left.
Here's what our planners in Washington don't want to admit. As bad as the Mullahs are, most Iranians support them.
Except not really. For its faults, the Islamic Republic is a known quantity. People you could sign agreements with and expect them to keep them.
The same could not be said of a regime run by the IRGC, which is already stepping into the void left when we killed all the Iranian leaders.
Nor do I. But the problem isn't just the top leadership. It's the middle leadership, and the person on the street. If there were Iranians who didn't think we were the "Great Satan" before we inflicted all this misery on them, they certainly think so now.