A year-and-a-half ago, we argued that the Syrian government was going to very slowly lose the war. We argued that the Assad government in 2012 (unlike France in 1958, facing its own civil war in Algeria) lacked the manpower to successfully occupy the rebellious territory. It would therefore face a war of attrition that would wear down its ability to field forces. Eventually the fight would become unsustainable.
And it is not just manpower. Other resources for the civilian economy are running dangerously short.
The question is whether those constituents see the war as an existential fight or simply as a pointless battle to re-establish control over regions about which they care nothing. If the former, then the current troubles will pass and the regime will fight on, albeit not to victory. (Defining victory as control over the prewar territory of Syria.) If the latter, then the government is in trouble.
The Islamic State was a existential and ideological threat to your average Syrian in the street, practically without regard to sect or ethnicity. But the United States is destroying the offensive ability of the Islamic State. Unless Al-Nusra emerges as a serious threat (which could happen) then the Assad regime is unlikely to be able to call upon its constituents to make the kind of sacrifice that, say, the Soviet people made against the Nazis.
So unless an existential threat re-emerges, then 2015 is when the violence will start to diminish. (Not end.) The government will either begin negotiating cease-fires or start to implode; our bet is on the former.