Will Turkey Overrun US Lines at Tall Abyad?, page-26

Given the three options at the foot of that article, I suspect option two, ostensibly until a political settlement that everyone is happy with in Syria and the US are sure that Turkey won't roll over the borders without the Syrians and Russians coming to the SDF's aid.
Option three is a sticky one. Not sure how that can be accomplished unless Russia is onside as Assad appears happy to have Iranian militias running all over the place and setting up bases and manufacturing plants. Russia unlikely to want to push Iran out of Syria as they are a key long term ally.

Looks like it's going to tricky in the area for many, many years yet.