Dunno... Iron Dome seems to be working pretty well for Israel right now, and it would have plenty of warning on an ICBM. Saudi Arabia with no Iron Dome has a lot more reason to be nervous. They have Mecca and any serious jihadi country would literally kill for it. Saudi Arabia might end up begging Israel to help it attack Iran.
The Iron Dome is okay to destroy regular rockets sent by Hamas in Gaza or by Hezbollah in Lebanon or by Syria near the Golan Heights, but the Dome doesn't destroy all of them, some get through. A nuclear bomb is meant to explode in the air over the target, so intentionally blowing it up over land is the same as it exploding on its own. Israel has to destroy the nuclear facilities in Iran before a nuclear bomb can be sent.