Iran has many avenues to retaliate against a pre-emptive Israeli strike
In the end, a successful attack would not eliminate the knowledge possessed by the project’s scientists, and it is possible that Iran, with its highly developed technological infrastructure, would be able to rebuild the damaged or wrecked sites. What is more, unlike Syria, which did not respond after the destruction of its reactor in 2007, Iran has openly declared that it would strike back ferociously if attacked. Iran has hundreds of Shahab missiles armed with warheads that can reach Israel, and it could harness Hezbollah to strike at Israeli communities with its 50,000 rockets, some of which can hit Tel Aviv. (Hamas in Gaza, which is also supported by Iran, might also fire a considerable number of rockets on Israeli cities.) According to Israeli intelligence, Iran and Hezbollah have also planted roughly 40 terrorist sleeper cells across the globe, ready to hit Israeli and Jewish targets if Iran deems it necessary to retaliate. And if Israel responded to a Hezbollah bombardment against Lebanese targets, Syria may feel compelled to begin operations against Israel, leading to a full-scale war. On top of all this, Tehran has already threatened to close off the Persian Gulf to shipping, which would generate a devastating ripple through the world economy as a consequence of the rise in the price of oil.
Israel would face the same limitations and uncertainties that exist for the United States in any strike on Iran's nuclear capabilities, with the added risks of having far less capacity than the U.S. military and the risks of being abandoned by its fragile alliances while setting off a regional war.