Angelo is right that Putin’s immediate objectives are protecting the Russian naval base and assuring Russia’s presence in the Alawite area of what used to be Syria.
However, both David and Angelo are overlooking another player in the Syrian saga. Iran has decided to intervene directly in the Syrian conflict, sending Revolutionary Guard troops to fight Assad’s enemies. they also did not mention the Russian takeover of a Syrian air force base. These are extremely serious events. Prime Minister Netanyahu is in Moscow as we write, and one of the main issues he will bring up with Putin is the introduction of advanced Russian weaponry into Syria. However, Putin can perfectly well put Bibi at ease while preparing to do exactly that through Iran.
In the past several months several convoys of military equipment sent from Iran to supply Hezbollah in Syria have been attacked and destroyed by the Israeli Air Force (IAF). If there is, as appears likely, an informal alliance between Iran and Russia vis-à-vis Syria, then Russians fighter planes stationed in Syria would be available to intercept Israeli planes and prevent them from attacking supply convoys in future. It is highly unlikely that the IAF would engage Russian fighters due to the obvious diplomatic implications of such a combat.
All in all, the Russian and Iranian maneuvers represent a game-changer in the Levant, with or without Assad. The two informal allies might well
dump Assad and replace him with a compliant general, who will limit himself to consolidating the Alawite coastal strip.