Afrin is going to fall. That's inevitable. And when it does, Turkey will control a significant portion of Syria's northwest-- from the border with Iskandarun/Hatay all the way to Jarablous. This is not a pretty picture. 
I should clarify, that picture is a worst case scenario for the short term. I put Tel Rifat in a slightly different shade of blue bc I'm not sure if the Turks + FSA will take it, I don't think the SAA would let them have Menagh airbase.
This Turkish occupation of the northwest could last for years. The Turks aren't just going to give this land back to the Syrian government-- they'll keep it as a "security zone" like they have been with Euphrates Shield already, or like Israel's occupation in South Lebanon.
This raises a lot of big questions. First off, will Turkey stop with the northwest? I doubt it. The original Euphrates Shield operation was a bit of a drag, but Olive Branch has been much quicker, esp in the last few weeks. With this kind of momentum, why would they stop?
After Afrin, Erdoğan says that Turkey's next conquest will be Manbij. The U.S. has been talking about a potential "settlement" w/ Turkey for Manbij, so it's possible that U.S. troops, the biggest reason Turkey hasn't already taken Manbij, could leave the area.
Manbij occupies an odd place in the whole "Rojava system"-- it's not a majority Kurdish, not even close, and from what I understand it wasn't part of the elections in Rojava bc it's technically not part of the self-declared federal system like the Afrin and Hasakah areas are.
I always thought that the sensible thing for them to do would be to give Manbij back to Damascus as quickly as possible. There have been rumors of negotiations between the PYD and Damascus regarding Manbij, but I haven't heard seen anything new about that in weeks.
If the U.S. pulls out of Manbij the Turks + FSA could easily take it, esp if Russia allows Turkey access to that airspace. If the PYD has any sense, they'll make a deal with Damascus to prevent the Turks from taking Manbij, which would be bloody and humiliating for them.
If Manbij is handed back to Damascus-- * that's a big if, the PYD may still be too stubborn to get what's going on here-- the next logical target for Turkey would be Kobani. If, at that point, the PYD STILL hasn't made a deal, then their stubbornness will be the death of them.
One of the biggest mistakes the PYD made was thinking they could play both sides-- the U.S. and Russia. You can't do that in Syria. You have to choose. The way Russia sees it, the PYD picked America. So they said "alright, fuck it" and opened up the airspace over Afrin to Turkey.
There was an article a while ago that had an interesting little anecdote about a Russian military officer trying to explain this to a YPG commander but I can't find it anywhere
Anyway, the PYD were idiots for not understand this earlier-- allying with the U.S. will make everyone turn against you, and if you want a long-term future in Syria, you need to work with Russia
