Jason, I believe that the poster was saying “too late” in regards to avoiding the loss of lives / cities scenarios you outlined.
You are correct that it won’t be ‘too late’ to reduce Iran to a cinder. But it may soon be too late to act to prevent Iran doing things that will necessitate us turning it into a cinder. Surely it would be preferable to act prior to it being ‘too late’ to prevent that being the necessary action.
Everyone discussing the matter needs to be fully aware of the international left's preferred plan and policy on Iran, which is first to dither diplomatically, exploiting the west's longing for peace, and then to claim that it is too late and nothing can be done and we will just have to get used to a nuclear Iran, and try to deal with it through talk, appeasement, and deterrence. Just as they proposed dealing with the communists throughout the cold war. This is Obama's policy and is in all the position papers of the left's foreign policy experts, and is the position driving the moonbats into the streets with their "don't touch Iran" posters. And it will lead directly to the deaths of millions of innocent people, not to "peace".
Do not give aide and comfort to them by talking about it being "too late", even hypothetically. Words mean things. Be careful.