To start with, the Iranian regime has every incentive to salvage what remains of the Joint Comprehensive Plan of Action (J.C.P.O.A.), to which not only America but Britain, France, Germany, China, and Russia are party. A true nuclear program would be expensive and difficult to restart, and would hardly bring popular support if it led to further international isolation. The smart move for Iran would be to invite China, Russia, and Europeans to continue inspections and to press for international relief from American sanctions.
Similarly, the other parties have every incentive to try to salvage the deal, both commercial and geopolitical. All of these countries want to do business in Iran, and none of them want to see Iranian nuclearization. When interests are aligned, there’s usually a deal to be made. If that deal excludes the United States, that’s probably a win not only for Russia, China, and Iran, but arguably for our European allies. It’s not like standing with the Trump administration is especially popular in London, Paris, or Berlin these days.