Syrians are dancing in the streets of Damascus and other cities, to celebrate the collapse of the hideous regime of Bashar Assad, the man responsible for an estimated 600,000 dead in a 13-year-long civil war — including tens of thousands viciously tortured to death in his dungeons.

Those still alive have been staggering out of liberated prisons, limping and running toward family and freedom.

“This is the moment of celebration,” I was told by the University of Oklahoma’s Joshua Landis, a Syria specialist with family in the country. He told me the dispirited Syrian army had faded away and let rebels win because they had been receiving little or no pay and no further support from their Russian and Iranian backers.

That's the good news.

The not so good news: No one is certain what kind of government will follow Assad in the weeks to come — whether it will help stabilize the region, including Lebanon and possibly Gaza, or further tear it apart.

The critical news, which may save Syria from a relapse into violence: Assad’s flight to exile in Moscow is a body blow to Iran’s ayatollahs and Russian dictator Vladimir Putin, for whom Syria had critical importance. It displays their increasing weakness and paints them as losers. It makes them more vulnerable to anyone who seeks negotiations with either.

President-elect Trump, take note.

The immediate post-Assad threat is that Syria might collapse into separate militia fiefs or into another civil war. Hayat Tahrir al-Sham (known as HTS) — the main rebel group that toppled the government in a lightning advance from the north — was once the Syrian branch of al-Qaida. Its leader, Abu Mohammed al-Jolani, broke with the terrorist group several years ago and is trying to soften his image. But Syria’s many minorities will have doubts.

“Jolani's going to have to reach out to all these different Syrian communities,” said Landis, hopefully.

I still recall my last visit inside Syria in 2012, during the Arab Spring just before the heightened civil war and Islamist kidnappings made journalistic access almost impossible.

With a Syrian translator, I visited a headquarters of a group called Ahrar al-Sham, inside an abandoned school, and the aggressive hostility of the fighters was only contained when a Belgian volunteer intervened. I soon left. I also interviewed moderate, unbearded civilian fighters who had set up militias because they wanted a democracy to replace Assad’s vicious rule.

How to coalesce secular Syrians, moderate Muslims, Kurds and Christians into a government with Islamists, and whether free elections will be possible is the huge challenge Syria will face.

Yet, what gives me hope is that the Iranians and Russians will no longer be able to bend Syria to their will.

After a popular uprising in 2011, Assad was only able to retain power because of intervention by Tehran, and later by Moscow. Although Syria has a religiously and ethnically mixed population, including a plurality of Sunni Muslims along with Kurds, Christians and other minorities, Assad belongs to a minority Shiite sect, known as Alawites, who have controlled the country for decades. Thus he was close to the Shiite regime in Tehran.

The Iranians sent thousands of fighters to Syria, comprised of their own forces along with Iraqi Shiite militias and even Afghan refugees living in Iran. Led by Iranian Revolutionary Guards officers, they were much more effective combatants than the underpaid and corrupt Syrian army.

Iran’s quid pro quo was Assad's permission to allow Iranian weapons and missiles to be trucked and flown from Tehran via Damascus to Hezbollah fighters in Lebanon to use against Israel.

Syria thus became a critical element of Tehran’s effort to encircle Israel with a “ring of fire” that included Lebanon's Hezbollah militiamen (along with Hamas in Gaza and Houthis in Yemen).

With Assad gone and Sunni Syrian rebel groups in charge, Iranians are fleeing the country. No more will they be able to transport weapons to Lebanon to be used against Israel. Nor will they be able to help the Alawite minority dominate the country.

Russia, for its part, sent planes in 2015 to bomb Syrian civilians and cities into rubble, just as they have done to Ukraine. Moscow was rewarded with a critical Mediterranean port in Tartus and a major airfield which helped support Putin’s expansionist ambitions.

Russia will most likely lose those bases, which gave them their only access to the Mediterranean and gave Putin an important Mideast role. His global access is thus shrinking. And Syria, hopefully, will be freed from his colonial games.

This means that the Islamists, and Jolani, will have to look to the moderate Sunni Arab world and to the West to help rebuild their country and resettle Syrian refugees who return. Which in turn gives those Arabs and Western leaders leverage to prevent any attempt to impose an ultraconservative religious state.

If this leverage is not used wisely, Jolani could become a threat, in a country where ISIS still has cells that are in touch with their counterparts in Iraq. If used wisely, Syria could revive and rebuild its shattered society.

Nothing less is owed to the thousands who died under torture during Assad’s rule.

Trudy Rubin is a columnist and editorial-board member for the The Philadelphia Inquirer.