The Syrian proxy war, has been a conflict by proxy prior to and since its outbreak. A proxy war fought by various vested regional and international interests for a spectrum of reasons both political, economic and sectarian.
Just because during the early stages of the conflict swathes of mainly Sunni Syrian troops were either bought off or found themselves ideologically compatible with the Salafist Wahhabi ideology being peddled by some of the regional sponsors of the conflict does not make it a civil war. Many if not most of the fighters the SAA and their allies face today are foreign fighters driven by money and/or ideology and self interest.
If the so called "moderate" opposition came out on top in Syria, stability is still far from sight and even if attained would only deliver the Syrian peoples with a Saudi-Arabia 2. If IS ever came out on top, we'd see Saudi-Arabia on steroids. Under Assad for all his faults, a melting pot of ethnicities, religions and cultures were able to co-exist in a relatively peaceful environment. We would not see the same if either the "moderate" opposition or IS were to come out on top. Look at Saudi-Arabia today, do you see the Saudi's respecting peoples ethnic, religious and cultural freedoms? Of course not. It's their way or no way and that is the worst outcome for Syria and its people.