I don't think it is that simple baron1. If Iran were to hit back they could do so in conjunction with Syria taking the opportunity to over-run Lebanon and onwards into Israel while the Palestinians invade Israel at the same time. Israel could find itself in a lot of bother trying to defend all it's borders. That is but one possible scenario of course.
The effect on us of course would be a massive spike in oil prices as middle eastern supplies are disrupted.
