The damage was done and any chance of pushing the US to coordinate forces in Syria evaporated.
Now Damascus is celebrating its biggest victory in over five years of war after recapturing control of the rebel bastion in the east of the city and dealing a hammer blow to those looking to oust Assad.
Here's how Russia helped break the stalemate:
Russian warplanes played a central role in bludgeoning rebel-held parts of Aleppo towards defeat with a brutal campaign that stirred memories of Putin's destruction of the Chechen capital Grozny in 1999-2000.
Although Assad's opponents finally gave up after Moscow said it halted air strikes on the city in October, Russia's bombers had already pulverised rebel defences for months, allowing the Syrian leader's forces to tighten their siege.
"Without Russia, nothing would have happened with Aleppo," said Alexei Malashenko, an analyst at the Carnegie Center in Moscow. "Everything was focused on Aleppo."
While Moscow insists its troops are not fighting on the frontlines, it admits it has military advisors on the ground supporting Assad's forces.
Malashenko said Russian advisors had played their role in helping the ground operation, noting that the death of a Russian army tank commander in Aleppo suggested Moscow might have drafted in some of its big guns to help out.
In addition to helping turn the tide militarily, Russia's presence also made sure of one thing: there would be no intervention from the West in Aleppo -- despite an outcry over the bloodshed.
As the operation intensified, Moscow demonstratively bolstered its hi-tech air defences in the skies over Syria and sent more warships -- including its only aircraft carrier -- to patrol the shores off the war-torn country.
For the Kremlin, victory in Aleppo can be seen as a stunning triumph to crown Moscow's first intervention outside the former Soviet region since the disastrous Afghanistan campaign.
Russia has helped thrust Assad into a position of strength while breaking the back of more moderate rebels groups supported by Washington and its allies.
Putin now appears the undisputed kingmaker in Syria and a key player across the entire Middle East. And he cut the US and Europe out of the loop on Aleppo by dealing directly with Turkey's Recep Tayyip Erdogan.
But the ferocious bombardment of Aleppo saw the West levelling accusations of war crimes that clearly stung the Kremlin and further strained its fragile ties with the West.
That was a blow for what many saw as one of the major initial aims of Putin's intervention in Syria: trying to ease his isolation over the Ukraine crisis.
"The main goal of the operation has been to force the West to speak to Putin," independent military expert Alexander Golts said.
"The situation has come full circle: Russia is now isolated because of the victory in Syria."
Blistering international criticism did eventually see Russia claim to halt its Aleppo strikes in October in the move the Kremlin called a "manifestation of goodwill".
But the damage was done and any chance of pushing the US to coordinate forces in Syria evaporated.
On the military side, the show of strength in Aleppo did not always go smoothly.
Moscow's ageing Admiral Kuznetsov aircraft carrier suffered two embarrassing mishaps within a month with two jets ending up in the drink.
Just as Russia was about to hail the fall of Aleppo, bad news emerged from elsewhere.
As Assad's troops focused Syria's second city, Islamic State group jihadists seized back control of the ancient city of Palmyra eight months after Damascus and Moscow retook it.
The loss was both a major blow for Putin -- for whom the capture of the World Heritage site had been a major propaganda coup -- and a potentially worrying sign of things to come.
The shock IS advance highlighted how tough Assad's forces will find it to keep a lid on areas they control -- and showed that Syria's protracted war is still far from over.
"With Palmyra captured for a second time, it's difficult to imagine that Aleppo will instantly turn into a peaceful city," Malashenko said.
"This big city will need to be controlled and there will need to be a huge Syrian army contingent with permanent Russian support."
The defeat of the rebels in Aleppo has so far not been accompanied by any progress towards a negotiated end to the conflict.
An emboldened Assad may now prove even more difficult for Moscow to bring to the table, which could hamper any efforts to scale back Russian operations there.
Key for the Kremlin will be how US President-elect Donald Trump approaches the Syria conflict when he takes power in January.
With the capture of Aleppo now a fait accompli, Putin and Assad may be hoping Trump stays true to his word and prioritises cooperation against IS over all else.