In order for there to be an all out war then they would have to send an invasion force here or else we would have to send thousands of troops there. They don’t have the means, and we are not going to wage a mass war against their country unless Iran does something really stupid like commit a mass terrorism attack. If they do something crazy like set off a Nuke then all bets are off.
That's what has the Saudis in an uproar. Rumor has it they've already bought a nuke from Pakistan. IOW a launch on the Saudi's will draw a launch on Tehran from Pakistan.