As far as the West is concerned, it would all hinge on what the United States so desires to do (as pathetic as it sounds) The British have run out of dosh and what is left of our ever shrinking military is already over stretched with commitments, so if the United States were to say "Let's take these bad boys out" Britain would be more then happy to tag along despite going deeper into the red but would need as many NATO country's to share the burden of commitment.
Also worth considering is the complexity of taking Syria as the Russians and Chinese could very well step in, so risking a powder keg of further escalation of conflict.
I think the only viable option rather than just sit back and do nothing would be for the West to just provide the Arms and humanitarian aid for somebody else to sort it out.
Finally, factor in that the West has little appetite now for yet another major sandbox crusade, as the last 21 years have provided us with almost constant death and destruction from the various punch ups that we in the West have been involved in.
Encouraging noises for the turks to create a buffer zone then give the nod for the Saudi's etc to finance training and turning of Disaffected Syrian army troops using the buffer zone as a base.
The Long Game!!!
Reality is more hot air from politicos and some ethnic cleansing who said History cant repeat itself.
Open middle east map....check.
Mark off all countries that are 'on side' (by force/finance or other).....check.
What's left.....Iran, Syria, and Yemen mainly, possibly Pakistan.
Mark allied strike and clutch bases in regions around the said problematic countries.....check.
Turn on TV to find out the coincidence that said countries are 'naughty'....check
It would be so easy to follow the western view that the poor, the downtrodden, the generics of the rebels is the path to follow, personally I am not too sure that we have got it right and to have the rebels win this conflict may not be the best thing for the western world, or indeed for anyone but the insurgents.
The government in power at the moment is comprised of all sorts of peoples, tribes and religions; the rebels are basically staunch Muslim supporters. And it is almost certain that they would follow a more fundamentalist path were they to get the upper hand.
Would this be a good thing? I personally think not. I am seeing a new Iran in the making. I think the Russians and the Chinese have got it right this time.
I suggest that we are going along the path that we have trodden so many times in the past; it has not always been the best for our own national interests.
Look at the crusades for example. What did we get from that in the long run there? What we got was yet again, more enemies to haunt us in the future.
I may be wrong of course but I would love to have some positive contradictory evidence that we have taken the correct path.