Just A Question: Now What?

So, it certainly appears that Bashar al-Assad no longer controls Syria.  There will be a lot of shaking out before we know who will control it going forward, or if it will even remain one country.

We have airbases there. Obviously their presence was negotiated with the Assad regime and/or it's predecessors.

What happens if one or more of the leading incoming factions tells us to take a hike? Any thoughts?