... at least partly. I think.
Syrian President Bashar Assad doesn't have to kill all of his opposition to win his civil war. If they decide to run away, that's just fine with him. Once German Chancellor Merkel invited everyone over for a prolonged pool party at her place, she created an opportunity for people in lousy situations, particularly Syrians, to get out and go somewhere better.
With that safety valve open for his enemies, it changed Assad's calculus and, by extension, Putin's. In addition to all of the other benefits of Russian intervention - primarily displaying America's weakness - it meant that all the Syria / Russia / Iran axis needs to do now is make life sufficiently unbearable for Assad's opposition and they'll flee to Europe. Winning the civil war is easier, thanks to Frau Merkel's kindness.
Finally, President Obama has pitched in here, too, in a big way. By now, it seems evident that America isn't going to intervene and save anyone in Syria. With the Russian air force pounding them and no help on the way from the Yanks, what's the point of sticking around?