'diplomacy' is a cynical farce
No one, neither the Europeans nor Russia and China nor indeed many of the Gulf Arab states, wants an escalation of what is a nascent war against Iran. They know that if the US mounts an enormous assault on Iran, the war will widen from Lebanon to Afghanistan. No rational person would support this.
President Rouhani made it clear to the United States that he could not understand who, other than his Foreign Minister, could be expected to speak for his country on international matters. Part of Iran's goal here is to maintain its sovereignty and dignity, and to select a new foreign minister would mean that Iran had buckled under US pressure. This is not going to happen. The Iranians are not going to replace Zarif.
But the Zarif issue is actually a red herring. Even before the sanctions on him personally, the United States showed no appetite for diplomacy. Iran spent several years negotiating with the five permanent members of the UN Security Council, as well as with Germany and the European Union, to produce the JCPOA, which was then ratified by the United Nations in 2015. After the US withdrew from the deal, Iran continued to indicate its desire for a diplomatic solution while Washington refused to come to the table.
The problem facing any negotiations is that the US position is untenable. The US wants to prevent Iran from exercising its right under the nuclear Non-Proliferation Treaty (1968) to enrich uranium even to low levels (4.5 %, which is far from the 90% enrichment needed for a nuclear weapon). It is this impossible position by Washington that stands in the way of a diplomatic solution. Until Washington accepts Iran's right under international law to enrich uranium for energy-generating purposes, there will be no permanent deal.
The Europeans indicated quickly that they were unhappy with the sanctions on Zarif. Carlos Martin Ruíz de Gordejuela, a spokesman for the European Union's foreign policy chief Federica Mogherini, said that they regretted the decision. The Europeans say that they will continue to work with Zarif to maintain open diplomatic channels.
Europe's tolerance toward Trump's shenanigans is being stretched, albeit to nowhere near its limits. The European Union, despite noises about its practical need for Iranian oil, has been unwilling to mobilize any political opinion on behalf of either the ailing JCPOA or against the wide unilateral US sanctions now on Iran.
Zarif has been working hard to build various coalitions around the world to prevent the United States from controlling the narrative. At the recently concluded Non-Aligned Movement (NAM) ministerial meeting in Caracas, Zarif held center stage. NAM, whose 120 member countries make it the largest political bloc inside the United Nations, has long opposed American unilateralism. In Caracas, they welcomed Zarif's declaration that unilateral sanctions by the US against Iran and Venezuela are a form of "economic terrorism."