Nice work with the quick time take down of the two goons accosting the woman. I managed to do this on the first try but I wasn't happy that the guy didn't notice me and retried it, just to fail about 30 times. :P I did find an easier way to take them out though.
If you wait for the left hand guy to step forwards to grab the woman, sneak behind his buddy and strangle him. Make sure you pull him away from the other guy otherwise he will see the body fall. Then just shoot the other with the sleeping dart. Not sure if rushing in to choke him would work, you'd need to be fast because he draws the sword on the woman and then it's too late, and he notices you if you shoot him with a sleep dart at that point.
As long as you choke the right hand guy when the left hand guy goes to grab, you should have plenty of time. However, it doesn't look as spectacular.