They now face what is likely to be the last showdown between Assad's forces and the opposition. Assad has vowed to retake the province, and pro-government media promise the "mother of all battles." If it comes to an all-out assault, it could bring a humanitarian crisis. Filled with displaced from elsewhere, the province in Syria's northwest corner is packed with some 3 million people, the most deeply irreconcilable with Assad's government and including some of the world's most radical militants. They have little option but to make a stand, with few good places to escape.
"Currently, all (opposition) from around Syria came to Idlib. The only solution is to fight. There is no alternative," said Firas Barakat, an Idlib resident. The 28-year old said that for years he has dedicated himself to civilian opposition activities, but now he must take up arms.
The opposition capture of Idlib in 2015 signaled the low point for Assad's government during the course of war that is now nearly 8 years old — a time when rebels controlled large parts of two main Syrian cities, major highways, border crossings, dams and oil resources.
Russian and Iranian backing enabled Assad's military to claw back territory. Most recently, it scored a victory with heavy symbolic resonance in the south, recapturing Daraa, one of the first places to rise against Assad's rule in 2011.
Around a third of the country still remains out of government hands in the north and east, most of it held by U.S.-backed Kurdish-led forces that wrested it from the Islamic State group. But Idlib stands as the last significant enclave of the armed opposition that rose up dedicated to ousting Assad.
"When we saw the resistance collapse in the south— and we thought it never would give it was the first to resist the government — fear really prevailed here," said Barakat. Squeezed, the opposition is desperate. But its forces are not small, and their territory is not tiny and sealed off as other opposition holdouts were. That portends a complex and difficult battle.
The number of fighters in Idlib is estimated at several tens of thousands, including thousands of battle-hardened militants from al-Qaida-linked groups and from China's Turkic-speaking Uighur minority.
Although the al-Qaida-linked group dominates, other non-jihadi factions have maintained their presence, including some of the earliest forces to take up arms against Assad. With Turkey's backing, they have formed a "National Liberation Front," excluding al-Qaida.
Idlib has seen a wave of lawlessness and assassinations among the various factions, including shootings and car bombs. Saeed al-Nakrash, a rebel leader originally from near Damascus, was kidnapped and held for 50 days. He blamed al-Qaida-linked militants and said his family paid $75,000 for his release.
The opposition-held area abuts the Turkish border on the north and west. Though Turkey has built a wall, the border remains porous, providing a supply line for fighters. That wall could be overwhelmed if massive numbers try to flee Idlib.
To the east is an enclave held by Turkish-backed Syrian fighters, a possible escape route for anyone fleeing, though it is already overwhelmed by displaced. Rumblings have started. Activists report government reinforcements arriving at Abu Dhuhur air base in eastern Idlib, which Assad's forces seized early this year. Troops have been shelling Jisr el-Shughur, a strategic opposition-held town overlooking the government stronghold on the Mediterranean coast.
Just how ferocious an offensive turns out to be depends on diplomatic maneuvering among the power players — particularly Russia. It appears reluctant for an all-out assault. Russia is juggling between longtime ally Syria and its new friend Turkey, which has become central to the political process Moscow is leading to try to resolve the conflict.
Assad vows to restore all of Syria to its control. Turkey fears an assault will send a flood of refugees — and militants — swarming to its border. Under a deal with Russia and Iran, Turkey has deployed around 1,000 troops at 12 observation points around Idlib to monitor a cease-fire, effectively standing between government forces and the opposition. It is part of a "de-escalation" zone in the province that ultimately aims to root out al-Qaida-linked groups as a basis for a future political process.
Turkey warns that a wide-scale offensive will wreck Russia's efforts. Its deployment in Idlib is a "trip wire that will start to tug at the (agreements with Russia) if you try to walk through it," said Aron Lund, a Syria expert with the Century Foundation.
From the other side, the Syrian government is testing the Russia-Turkey relationship. During the latest meeting in Russia in July, Syria's U.N. ambassador Bashar Jaafari blasted Turkey, saying it has failed to weed out extremists from Idlib.
Jaafari said Damascus encourages reconciliation with rebels, but not with al-Qaida militants — adding that it is Turkey's responsibility "fight terrorism." "If Idlib returns in reconciliation, this is well and good. And if it doesn't ...the Syrian army has the right to restore control over Idlib by force."
That makes Russia's stance critical, said Sam Heller, a researcher with the International Crisis Group. "Ultimately what determines the survival of Idlib may be external, and they relate to these geopolitical considerations," he said.
Russia has already said no wide offensive is expected. That has raised speculation over a limited operation to control Jisr al-Shughur or the main highway running through Idlib. Wael Olwan — a spokesman for one of the strongest Turkish-backed Syrian factions, Faylaq al-Sham — said Turkey working with Syrian allies can "dissolve" the al-Qaida-linked factions.
But, he said, "I am not optimistic that Russia can hold back the regime forces long enough for Turkey to dismantle the radical groups."