It is a strategy and tactics question. But it is hard to answer, because it relies upon seeing the future (see below).
The answer is that it depends to what extent Russia withdraws. Think of it in terms of a bar fight or a street fight. If a fight breaks out, and the stronger man comes in with the weaker man, he might throw a few punches until his foe goes down, and then move back six or eight feet to see what happens. If the foe slinks off, then fine; but if the foe comes back, he can re-engage. In neither case would one think the stronger man has been seen off or lost face, unless (in this analogy) the rebels were to somehow deliver the knockout. Similarly, when Russia "starts a withdrawal," we have to wait and see: do they immediately steam the whole Baltic and Northern fleets back home? Or do they keep some of them in the area to wait and see what happens? It is expensive to do that (especially since Russia has only a small and underdeveloped naval station in Syria), and I think the northern Black Sea has the nearest Russian base besides that one. Given that Russia has no other foreign naval port besides Syria's (whether it is underdeveloped or not), I don't think there's a question of Russia wanting to "keep their face if they withdraw"--they have shown a bulldog's stubbornness in insisting on keeping their Syrian connection active, and they've hardly been seen off. They have consistently had more control in Syria over the last several years than the NATO powers have, for instance, dictating terms as to when cease-fires would and would not occur, and engaging in airstrikes at will.
Also, the question presumes that western countries would indeed keep giving support to the rebels after such a battle. If (as Russia hopes) they were dealt a knockout blow, there might not be enough rebels or enough rebel strongholds left for the west to be able to arm anyone, or it might no longer make sense to keep arming those who are there. Western countries might well adjust their own support, based on the success or otherwise of such Russian offensives.
I don't think Russia sees itself losing this struggle; for the moment, I can't find much evidence to disagree with that either.