There are two possible outcomes if it is indeed proven that the Syrian government has indeed used chemical weapons on its own people.
Possibility 1: This will set the standard for surrounding countries, causing them to follow suit. Surrounding countries will use chemical weapons against their own people for manipulation, crowd control, enforcement of government policies, etc.
Possibility 2: An infectious series of riots will break out within the surrounding countries causing distress among the international community. I would even dare say, that the surrounding countries would go as far as to attack Syria.
These are just a few speculations. Of course, I'm no war room commander nor a politician, but there's my two-cents.