Without electricity, there is no modern life. There is no ability to communicate, pay salaries, run a business, have running water, etc. Without fuel, there are no logistics; there is no capability to transport an army. Nor is there an ability to transport food, people will starve; it would cause an enormous civilian crisis, and this would cause massive riots bigger than the ones seen in January.
The Iranian government would have no ability to coordinate a response, and Iran would collapse within a week. The country would devolve into chaos, into paramilitary factions, and a civil war would start, similar to in Syria.
The US and Israel have been sitting on this the entire time. They don't want to do it, because it would cause near permanent economic damage to Iran.
Once Iran showed it had no ability to prevent the US/Israel from doing a indiscriminate bombing campaign, it was clear the US and Israel could always win this war through this outcome.