If the rebels do have access to chemical weapons, then this is an obvious setup. After the UN leaves with Assad’s chemical weapons, the rebels stage another false flag attack, Obama claims Assad was holding out on the UN, and it’s back on.
I don't think Syrian CW can be transported. They have too much of the stuff, and who knows how many of those bombs are unstable and ready to spill the contents. The weapons will have to be destroyed in Syria, using US or Russian technology, at a facility that is built for the job. It will take years. While that's happening, the CW depots will be guarded by international forces. Assad will have a pretty good alibi.
The argument of "he hid one or two barrels of Sarin" won't work because it's impossible to disprove. If someone is murdered we don't arrest the neighbor just because he could have had the weapon. We investigate to find out if he did have one. Anyone can have a barrel or two of Sarin - it's a pretty old chemical, well known and well understood. In case of a chemical attack, like the one that happened recently, the proper response would be a police investigation that discovers facts, clues, evidence that points to specific people. And besides, what is the military value of a few chemical bombs?