The red, white, green and black flag of the Free Syrian Army flew over Damascus on Sunday as thousands of residents lined the main square in defiant bursts of jubilation - after President Bashar al-Assad relinquished his grip on power and for the time being nothing is known about his fate

Over the past 11 days, a rebel alliance charged through Syria in the boldest challenge to Assad's rule in years — after decades of brutal rule by the Assad dynasty marked by fighting, bloodshed and a political crackdown.

"This is an important moment, not just for the Syrian people, but for the people of the Middle East, Lebanese, Palestinian, Syrian or otherwise," said Firas Maksad, a senior fellow at the Middle East Institute based in Washington for CNN.

"This is a regime that for more than 50 years, under the mantra of freedom, unity and socialism, oppressed, tortured and disappeared millions in Syria.

Now, as the anti-regime coalition begins dismantling Assad's army and lays out its vision of a post-Assad Syria, experts wonder whether the next phase will be a new dawn for a people suffocated by a brutal autocracy — or whether sectarianism will bring another kind of authoritarian rule.

Syria's armed opposition ultimately plans to form an institution-defined government and a "popularly elected council," Abu Mohammad al-Jolani, the militant figure leading the latest rebel movement, told CNN. He heads the dominant group in the coalition, Hayat Tahrir Al-Sham (HTS), a former al-Qaeda affiliate.

Assad has not been seen or heard from since rebels declared Damascus "liberated" after sweeping through the capital and capturing key sites. The whereabouts of his wife and two children are also unknown. Since the uprising began and rebels made rapid progress across the country, Assad has kept a low profile.

After meeting with Iran's foreign minister last weekend, he vowed to fight "terrorist organizations" but has otherwise made few comments as rebels seized major cities.

On Saturday, as rebels surrounded Damascus, a source told CNN that Assad was nowhere to be found in the city.