In reply to MargieB:
> Would it be right to assume that territiory north of the Euphrates in essentially sunni territory. This means it cannot be taken by Russia with the current Syrian political structure with Assad as they could not retain political control of it after it was taken. Perpetual turmoil. This leaves two ideas left, : Russia insists on a new inclusive government but also insists Assad goes and then it retakes the north with tribal agreements. Or northern sunni syria is taken by a UN force{Un does in a way include Russia} to produce a semi autonomous situation in northern Syria with UN protection. The latter depends upon finding Syrian moderate support to run it afterwards.
I think that you overestimate the influence that Russia has. The majority of pro-Assad effective combat troops are Iranian, Iraqi or Hezbollah. The new regime in Damascus would have to be acceptable to them, and it is hard to see how any government that was, could work with Sunni tribes. Horrific as ISIS is, I imagine that the average Sunni Syrian feels safer under them than under a Shiite militia.
Russia's current strategy in Northern Syria seems to be an alliance with the YPG that they hope will allow a Kurdish state that encompasses many currently Sunni regions and we are now seeing real fighting between the YPG and FSA, which Turkey is actively involved in. I'm not sure that even Russia sees this as a solution, but I don't think that they have any particular desire to end the war if they can keep their costs down sufficiently. Very similar in some ways to Ukraine and Georgia.
Post edited at 11:35
