I doubt Russia or China would do anything militarily...buuuuut...
It was doubted that China would intervene in North Korea until they did
It was doubted that the death of an Archduke would start World War One, until it did.
So I can't say anything with much certainty, but rationally, it would not make sense for either of them to do so...but equally, rationally, it would not make sense for us to launch military attacks on Syria, nor for Assad to have used the chemical weapons in the first place. So rational thinking is not necessarily in popular demand amongst the powerful at this time.