Israel is worrying about after Assad due to extremists who are fighting inside FSA so doesn't want a regime change. Also a Shia block (Lebanon-Syria-Iraq-Iran) can stay away to Turkey from gulf countries and this is most important aim of Russia. Clearly they don't want a new campaign in Caucasus. Iran wants to use to Lebanon and Syria against Israel in a possible conflict so still supporting criminal Assad at the cost of losing Ummah's support. Until USA decides to attack Iran, fight will go on in Syria.