But given fears of instability at a time when the Islamic Republic is facing internal protests, a weak economy, endemic corruption and tensions with Israel, analysts expect little change in Iran’s foreign or domestic policies. Mr. Khamenei has set the direction for the country, and any new president will not alter it much.

The system is “already on a trajectory to make sure that the successor of the supreme leader is completely in line with his vision for the future of the system,” said Ali Vaez, the Iran director at the International Crisis Group.

He described “a pretty hard-line vision” in which key areas of foreign policy, like support for regional proxy militias and developing components for a nuclear weapon, are not going to change.

Whoever is chosen as the next president, Mr. Vaez said, “has to be someone who falls in line with that vision, a subservient figurehead.”

Ellie Geranmayeh, an Iran expert with the European Council on Foreign Relations, also sees continuity on key foreign policy issues, including regional issues and the nuclear program. “These files have been under the control of Iran’s supreme leader and the I.R.G.C.,” she said, referring to the Islamic Revolutionary Guards Corps, “with Raisi having little influence during his tenure as president.”

“Raisi was certainly useful to some I.R.G.C. factions,” said Ms. Geranmayeh. Unlike his predecessor, Hassan Rouhani, Mr. Raisi, a more conservative loyalist, “did not challenge the I.R.G.C. either on domestic or foreign policy issues,” she said.

But criticism of Mr. Raisi’s performance as president had already raised questions about whether he was the best candidate to succeed Mr. Khamenei, she said.

Mr. Raisi’s main rival was considered to be Mr. Khamenei’s son Mojtaba, 55, whose candidacy has been harmed by the aura of a monarchical succession.

Mr. Raisi’s death may give Mojtaba Khamenei an easier path to succeed his father. But the internal workings of Iran’s religious and domestic politics are deliberately mysterious, and the decision in the end will be made by a council of senior clerics known as the Assembly of Experts. Though Mojtaba Khamenei is considered to be a favorite of the clergy, they may yet decide to pick one of their own or have more of a collective leadership.

His father, the supreme leader, had worked hard “to reduce the unpredictability within the system by grooming President Raisi to potentially be his successor and now all of those plans are out of the window and they’re back to the drawing board,” said Mr. Vaez.

Externally, the challenges are also steep. Iran and Israel attacked each other directly in April, even as Israel is already fighting Iran’s military proxies — Hamas in Gaza and, less vividly, Hezbollah in Lebanon. Iran also sponsors the Houthis in Yemen, who have attacked shipping in the Red Sea.

Iran has worked to avoid a larger war between Hezbollah and Israel, and a direct conflict with Israel is also something the Islamic Republic can ill afford.

It has been holding intermittent talks with the United States on de-escalating the regional conflict and on the future of its nuclear program. The death of Mr. Raisi threatens to complicate those talks, too.

“While there will be no love lost in D.C. for Raisi, instability in Iran would come at a bad time,” said Trita Parsi, an Iran expert at the Quincy Institute for Responsible Statecraft, making “escalation prevention all the more difficult.”