If you need Putin to come in and incinerate your citizens for you then you are no longer a strong man controlling your country you are a tinpot dictator propped up by foreign powers. That rarely ends well. The "he protects monitories and only mustard gases the majority" is a pretty weak argument as well.
When will we learn to stop propping up repressive dictators who murder their own people? Assad will not be able to put his country back together. Yes it is very likely that whoever ends up taking over will be as bad or maybe even worse but if he is nothing more than a puppet for Russia he won't last. The middle east is no more willing to see Russia control a Muslim country than they are to see the US control one.
If Putin is willing to commit enough forces and if Obama is balless enough to stand by and let him do then Assad might be able to regain temporary control but it won't last. Supporting him just prolongs the violence and upheaval.