And if ISIS reach the coast?
For those suggesting that 'the West' withdraw and allow the local groups to slog it out, what happens if ISIS reach the Mediterranean coast? That would signal an Israeli involvement far greater than anything we have seen since 2006. And Turkey, would they be finally prodded into some action? Al Assad Bashir has to go; any legitimacy he had went when he began to use CW.
Sadly, whether we like it or not, the origins of this conflict go back 100 years with the carve-up of the rotting Ottoman Empire and great-power rivalries at the time (principally between France and UK). Then add US adventurism to the plot 90 years later and oil-soaked desert fiefdoms...what could possibly go wrong?