I am fascinated that this very important subject is not being better discussed.

If the West goes for "regime change" as they did in Libya and Iraq, obviously life will be very much worse for the Syrian people.
Iraq and Libya have descended into lawlessness and terror, the same fate awaits the Syrians especially minority groups so beloved of the Mudcat "liberals", but more importantly, as Sanity has noted, Russia has bases there and would be involved in protecting those bases.

What retaliation can we expect in return for supporting or in the case of the USA instigating an attack?

Would it be military or economic? Would China become involved?
I'm sure most....even here, would see it as a no win scenario.