Interesting question. If Iran are attacked by the US then obviously they will be conquered within a few days. But the question is with the US in control of Iran's oil supply would it keep the supply flowing as it was or will they take more for themselves, or cut off oil to Russia or maybe China, or to all three. This is the real question. Personally I think the invasion of Iran won't happen, all the nuclear scientists are being assassinated and they also know if they actually build a nuclear weapon Israel and the US will invade them.
If they go through with building a nuclear weapon which is unlikely as Israel's military is far superior, and is constantly watching them. So they wont build a nuke and oil supplies wont be reduced to anyone in the US Russia China or India as all those nations are too powerful to have Iran messing them around. If they want they could force Iran to give them oil.
Iran has no hold over anything, they could be allowed to build nuclear weapons by the US and Israel but they wouldn't be able to use them against any of the said countries as their missile technology is so massively inferior that they could launch 100 nukes literally and Israel would shoot them all down in space with anti ballistic missiles and lasers. Think about how high - tech the Israeli military is then you realise Iran's position, then you have the US which can also shoot them down with warships nearby.
Iran can't do ****, if people want their oil they will get it, and if they don't want Iran to build nukes they can stop them, even if they do they can't use them.