So now there is a deal between Russia, the US and (presumably) Syria, in the sense that Russia must have secured some sort of promises from Assad that he and the Syrian military would comply with this. But there's no real certainty that this is going to work. I could see all sorts of ways that Syria might try to evade or quibble with upcoming inspections or retrieval missions.
Ironically. key Syrian opposition groups have already slagged this arrangement, calling it a bluff. And they are right that it doesn't solve any of the political issues, whether on the ground in Syria or outside. It's essentially a move to kick the can down the road, and risks exacerbating the conflicts, making them more bitter and harder to handle.