It's a complicated subject. Iran is under fewer sanctions that it had been in the past. For example Iran is in preliminary talks to buy Russian SSJ-100 airliners. The airliners have US components (22% allegedly) which blocks current sales, but a "Russified" variant (the SSJ-95R or SSJ-75 depending on who you ask) is being developed for customers like Iran, where US components will make up less than 10% and won't require US approval for export sales. However the same airliner has plenty of European components, including Russo-French engines, which are a lot harder to replace. If the EU re-imposes full scale sanctions it will certainly limit Iran. Additionally Iran has a deal with Russia to get their nuclear fuel, use it, and then return the waste to Russia. Will Russia continue to sell Iran nuclear materials if they know that Iran could use it for weapons? Right now Iran is complying with the deal and not building weapons. The US looks aggressive, and Iran almost looks like the victim (their other "activities" notwithstanding). But if Iran returns to trying to produce nuclear weapons, the game changes. And given Russo-Israeli relations, and Russia's complex game across the Middle East, I'm not sure even they would stand by Iran if Iran went nuclear. I mean look at Russian and North Korea. They still have some bilateral trade, but the DPRK gets basically no real political support from Russia. And if even Russia won't support them Iran will end up in international isolation all over again.
I think the smartest thing Iran can do is stick to the terms of the deal, while complaining loudly about US unfairness, and meanwhile work with the EU, Russia, China, and anyone else who is willing, to undermine and circumvent US efforts in this department.
