If Assad hopes to control Damascus as part of a Core Syria based on the Alawite homeland in the northwest, he has to control the line of communication between the homeland and the capital.
Assad still doesn't have that control:
Syrian government forces have been locked in a bitter struggle to control strategic ground outside the capital, Damascus, and a highway along the Lebanese border leading to the northern coastline. Attempts by government forces to chase rebels out of the corridor leading north appear to have stalled[.]
Russia says that they would commit troops to the fight if asked:
Russia would consider a request from Syria to send troops if Damascus asks for it, the Kremlin's spokesman said on Friday.
And really, given the growing unease among Assad's supporters about the power that Iran has gained over Syria, having someone to balance the Iranians is looking pretty good to Assad these days:
But while Russia appears to have coordinated its military expansion with Iran, Mr. Assad’s other key ally, the move could also serve as a counterbalance to Tehran’s powerful influence in Syria, a phenomenon that has generated ripples of unease in some circles of the Damascus regime.
It doesn't look like Russia wants to do more than provide air defenses and ground troops for local defense. So it will be up to Iran to provide the manpower to fill out Assad's depleted ranks. How will that division of labor sit with Iran and the people they recruit to die?
Let Russia flail in Syria rather than save them.
It would be nice to generate some friction between Russia and Iran (and Hezbollah). And perhaps force Assad to choose between surviving in his Alawite homeland and holding Damascus.