1 And he will almost certainly be replaced by someone more radical and prone to war.

2  IRGC replaces them, mossad paints them as a target, IDF vaporizes them.

3 Now, there's a name I haven't heard in quite awhile. In fact, I didn't know he was still alive. Do we know if he even was? 

4 There are hardly any more radical than Khameini and the other leadership Bill. There is nothing to lose here. And as Mike says, they can send up the next guy to wind up raining body parts. Eventually the People will rebel effectively or a more moderate guy will come to power (being all that's left) and then we can deal. 
What we can't deal with is the current regime in power and never have been able to do so. The fact that they tried to assassinate Trump is proof that we aren't the ones who started this, and that this was going to have to be dealt with eventually. Do we wait until they get a nuke? They basically already have one; they have uranium enriched above 10%, the magic number. What they have been doing is holding off on testing so they can get a proper delivery system in place. They weren't satisfied with a Hiroshima-style gun trigger fission bomb either; they've been working on implosion devices because they get more bang for the buck that way and those are lighter so easier to deliver. We know North Korea build a bomb right under our noses and the Iranians are smart people. No doubt they've been doing virtual testing with their computers. 
But even if they NEVER get a nuke they still have cost untold numbers of lives and many Americans have died at the hands of their proxies. Where is the line? When is enough enough?
I get not wanting to send troops into Iran; that would be stupid. But this is the proper way to deal with them. We have a ready-made revolution in motion right now, and when the regime runs out of thugs the army will revolt. We've seen this kind of thing before, in East Germany, in the old Soviet Union, etc. 
I don't know about you but I'd rather not be looking over my shoulder all the time. Better to stomp them now.
BTW the Austin shooter had Iranian flags and photos of Iranian leaders in his home.