I don't think we're willing to do that.

I agree. In which case, we shouldn't be doing this at all. You're either in it to win, or you're not. If you're not, don't kill people for -essentially- no reason.

And even then, it might not work.

Absolutely. It would be a dice roll. But I think it would be the ONLY way -maybe- to accomplish it. Crushing their military wasn't/isn't enough. Dropping more bombs won't do it.

The discontent of the Iranian people is the only thing that could do it. But it would have to be pervasive and unstoppable. If their economy is functioning, that isn't going to happen. May not happen anyway (as you say, could be "rally around the flag"). But that's the only shot.

Otherwise we should just go home. We shouldn't even have started, but that horse has already escaped the barn.