through physical inspection within Iran that their only nuclear program would be to provide 3.67% enriched Uranium fuel for Thermal Nuclear Reactors that power their nation's electric power grid...which the IAEA inspectors verified. It was only AFTER Trump ripped the document up that Iran produced over 900 lbs of 60% enriched Uranium. So, as the attached IAEA document explains, the world could be assured that so long as the JCPOA was in effect, Iran would not be capable of producing a Nuclear Weapon.
As for "Sunset Provisions", the same levers that brought about the JCPOA in the first place (e.g. Sanctions and Frozen Assets) could be ramped up should Iran choose not to continue with it...all without loss of life, or economic chaos for all nations. Note that we could have then...and could still now...offer options for U.S. assistance (with continued IAEA oversight) to Iran in building out a peaceful nuclear power energy strategy...thus toning down the "Death to America" chants and maybe even find a pathway to Peace in the ME...just my thoughts.
Lets hope current negotiations head more in that direction, than the one Trump chose at the beginning of this needless war.
Link: https://www.iaea.org/newscenter/news/iaea-now-has-more-inspection-powers-in-iran-increased-knowledge-of-its-nuclear-programme-director-general