Yazata response does not take into two important factions, ISIS and the Kurds. Between them they control a large area of the country. The Kurds are probably the "best" on our (USA) side, but unfortunately Turkey doesn't trust them.
I was thinking of ISIS among the "rebels". They are just the smelliest of the bunch, weirdly apocalyptic, prone to scaring/alienating everyone around them by calculated atrocities, and currently in control of the most territory. Some of the other rebel groups aren't tremendously different in their determination to enforce Islamic law and oppress religious minorities. If ISIS captured Damascus and overthrew Assad, and achieved dominance over the other rebels, that would just be going from bad (Assad) to worse (crazy jihadists). But victory by some of the other rebel groups runs the risk of putting Syria in the same nasty 7th century place.
The Kurds are something else. They are their own ethnic group with their own language, not Arabs at all. (Indo-Europeans loosely related to the Armenians, I think, except the Kurds are Sunni Muslims while the Armenians retained their ancestral Christianity.) The Kurds don't really want to control all of Syria, since that would mean ruling lots of Arabs who would probably resent it and fight them. The Kurdish goal is to carve their own Kurdish state, Rojava, out of Syria. So the Kurds aren't going to overthrow Assad and they aren't going to suppress the other Arab rebels. Nor are they going to eliminate ISIS as Washington apparently hopes. They aren't going to do anything that will bring the Syrian civil war to a conclusion, one way or the other. As far as they are concerned, the Arabs will have to sort out the rest of Syria for themselves.
Eve if Assad and allies defeat the rebels, they still will have ISIS and Kurds to contend with.
If Assad hopes to enforce peace in Syria, defeating the rebels would have to include defeating ISIS. And if he hopes to enforce peace in all of Syria's territory as he once did, that would mean fighting the Kurds and getting rid of their Rojava statelet. Turkey might help him in that, since although the Turks loathe Assad (mostly because he's an Alawite and is friendly with Iran) they oppose the idea of a Kurdish state on their border even more (because most of southeastern Turkey has a huge Kurdish population that wants to join the other Kurds in independence).
I think that Turkey will be something to closely watch in upcoming months. The Turks are currently led by democratically elected but increasingly autocratic "moderate" Islamists and the country is rather unstable after the recent coup attempt and the purges that followed. They've swerved from shooting down a Russian jet fighter to flirting with Russia. And despite their having been (along with the Saudis and Qatar) the biggest source of funding and arms for the anti-Assad Syrian rebels, they might swerve again if Assad looks like he is winning to join him in common cause against the Kurds.