Officials and analysts say that much would depend on how and when the talks fell apart. Both Iran and the United States — along with its five negotiating partners, France, Britain, Germany, Russia and China — are reluctant to walk away from the talks, meaning they are likely to drag on even if they don’t meet the March 31 deadline.

Missing that deadline, a goal set in November for a political agreement that would leave technical details to be resolved later, would have no practical effect. The deadline of real consequence is June 30, when an interim deal now limiting Iran’s nuclear program will expire.

And even if the negotiators make Tuesday’s deadline for a political agreement that could be a vague placeholder to buy more time, the talks could still break down later over the technical details due by June 30, as well as continuing friction over Iran’s policies in places like Yemen and Iraq.