I am guessing that there will be three ways this will come down:

1. The Syrian government forces will be on the receiving end of joint US-French Naval and Air Strikes.
   
2. Nothing -- no one will intervene and Assad and his government will maybe use Sarin gas again. How long before Sarin gas attacks expand into Turkey, Jordan, or Israel? Turkey is a NATO member and the Israelis maybe have 200 nuclear missiles.
   
3. The Syrian Rebels and Syrian government's army continue to fight on and there are 250,000 dead next year and 4 to 6 million war refugees for Turkey and Jordan to deal with.
   

There are no good alternatives -- pick your poison ..