(CNN) -- The rocket that hit Yemen's presidential compound Friday and injured President Ali Abdullah Saleh achieved what months of mediation had not -- loosening Saleh's viselike grip on the presidency after 33 years.
Late Saturday night, Saleh arrived in Saudi Arabia for medical treatment and the nation's vice president assumed his powers.
Diplomats in the Gulf say the Saudis are not likely to help Saleh get back to Yemen, even if he were well enough to travel. It is possible he will return, but the celebrations that erupted in the streets of Sanaa Sunday suggest that after four months of sometimes bloody protests his opponents think they have seen the back of him.
Which begs the almost unanswerable question: What next for Yemen?
No one seems optimistic. British Foreign Secretary William Hague said Sunday he was "very worried" by the situation.
"It could become a much more serious threat to our own security," he said. The worst-case scenario is an implosion -- Somali-style -- giving al Qaeda living space next door to Saudi Arabia and adjacent to one of the world's most important sea-lanes.
The regime has been dealt a serious and perhaps irreversible blow. The rocket that wounded Saleh also left several members of his government injured, including the prime minister. Several of them are also in Saudi hospitals.
The tribal alliance that had taken up arms against Saleh seems to be the beneficiary, but Yemen is a country awash in weapons -- and they are held by competing elements within the security forces, by powerful tribal confederations, by Islamist militants and secessionists in the south.
Yemen has never been a cohesive state; even after (violently) unifying North and South Yemen in 1994 Saleh governed through deals with powerful tribal leaders.
Many have benefited from a complex web of patronage; few are likely to surrender their spoils willingly. A U.S. diplomatic cable from 2005 holds true today: "True power still derives from the military and the tribes."
Saleh always made sure close relatives were prominent in the security forces. Today his son Ahmed Ali Abullah Saleh, long groomed to be his successor, and his nephew, Yahya Muhammad Saleh, command the most effective units -- and may yet decide to make a fight of it. Ahmed commands the Republican Guard and Yahya the anti-terrorism Central Security Force. Other relatives are also military commanders -- in 2005, 31 of the president's cousins led army units.
Ranged against them are leaders of the al-Hashid tribal federation -- of which Saleh is a member. One by one they have deserted the president as he concentrated influence and money within a small clique of family and associates.
They include Hamid al-Ahmar, a leader of the Islamist party Islah and a prominent businessman, who has long been an opponent of the president. His brother Sadiq, the current sheikh of al-Hashid, called on Saleh to step down after the shooting of dozens of protesters in March.
For generations, the Yemeni state has done little without the al-Ahmars' blessing. Sheikh Abdullah Bin Hussein al-Ahmar, who died in 2007, was one of the few Yemenis to command widespread respect -- a man often described as the father of modern Yemen. He was an opposition leader but also speaker of the Parliament, and Saleh was careful not to cross him. Today, there seems no one of similar stature.
The most powerful man in Yemen now that Saleh is in a Riyadh hospital is probably Brig. Gen. Ali Mohsen al-Ahmar.
As commander of the First Armored Division, he dealt a possibly decisive blow to Saleh when he defected in March and took a chunk of the army with him. He then instructed his troops to protect the protesters in Sanaa. His units recently took over buildings near the presidential compound.
Saleh blamed al-Ahmar for the rocket that hit the presidential compound Friday. Other officials said only professional troops could have organized such a precise attack.
What makes this al-Ahmar of concern to Western governments is his links with radical Sunni Islamists. Yemeni observers say the Muslim Brotherhood has long been influential within al-Ahmar's military command and he is known for his antipathy toward Yemen's Shiites. A U.S. diplomatic cable from 2005 said that "Ali Mohsen's questionable dealings with terrorists and extremists would make his accession unwelcome to the U.S. and others in the international community."
Barak Barfi, a researcher at the New America Foundation, a think tank that focuses on terrorism in the Middle East and South Asia, noted recently that al-Ahmar "is married to the sister of Tariq al-Fadhli, a Yemeni who fought alongside al Qaeda leader Osama bin Laden in Afghanistan. When more than 4,000 Arabs returned from fighting the Soviets there, al-Ahmar organized them into units and deployed them in the 1994 civil war."
His decision to defect may have been motivated by personal revenge, if a U.S. diplomatic cable published by WikiLeaks is accurate. While he was trying to put down a revolt by a Shiite clan in 2009 with the help of Saudi air power, officials in Sanaa "accidentally" gave the Saudi air force the coordinates for al-Ahmar's command center, saying that it was a rebel camp. Luckily for al-Ahmar, the Saudis were suspicious of the information.
One of the few elements of Yemeni society not well-armed are the students who started the protests against Saleh back in January -- inspired by the uprisings in Egypt and Tunisia. Having made substantial sacrifices in the months since, they are likely to continue street protests to try to prevent their "revolution" being hijacked by a tribal bargain. But the young, educated middle class is marginal in this conservative and hierarchical society.
As April Alley of the International Crisis Group wrote in April: "Established opposition parties, Huthi rebels, some southern separatists, religious leaders, prominent tribal sheikhs, businessmen, and army commanders have joined the protests. Although youth and civil society activists welcome assistance in ousting Saleh, they are legitimately skeptical of the role that some of these forces may play in the future."
The main opposition parties, ranging from socialists to Islamists, grafted themselves onto the protest movement but have little in common except their animosity toward Saleh. Nor, with the exception of the Islamists, are they very well-organized.
Other figures who may play a significant role include the cleric Abdulmajid al-Zindani, who heads the Salafist (very conservative) wing of the Islamist party Islah. He is feared by liberal Yemenis.
Analysts say Saudi Arabia will now try to turn a shaky truce into a more substantive plan -- a post-Saleh transition leading to elections. That was at the heart of the plan devised by the Gulf Cooperation Council (of which Saudi Arabia is the dominant member) -- a plan Saleh accepted and then rejected.
But there is a real risk that the remaining Salehs and the al-Ahmars may yet seek to settle issues at the barrel of a gun.
For now, Vice President Abd-Rabbu Mansour Hadi has taken over and commands the armed forces and security services. Vice president since 1994, he has in recent weeks said (tactfully) that he doesn't want the top job. And as a southerner, he doesn't have much of a power base.
Ali Abdullah Saleh became president when Jimmy Carter was in the White House. He has outmaneuvered every rival since. One U.S. diplomatic cable published by WikiLeaks said simply: "When asked for names of potential successors, Yemenis are unable to come up with a single potential candidate." Even the most powerful men in the land may prefer to be kingmakers than kings.
Whatever power structure emerges, Yemen's next leaders will face daunting tasks -- inheriting a state where oil revenues have declined and the economy is in ruins, where poverty is endemic and where a young and rapidly growing population faces a chronic shortage of water. Not to mention percolating rebellions in the south and north, and a well-entrenched affiliate of al Qaeda.