Those area's are easier for mobile movement. When you hit Mountains, it bottlenecks movement. Look at Korea,Okinawa, Italy for example.
The rebels are nothing like the armies of Italy, Japan and Korea, those armies were unified and well supplied, no matter how tough the terrain the rebels are logistically and fundamentally flawed in terms of command structure, once one chip falls it'll become a domino effect, I can only see a little trouble in Latakia and Jabal Turkman but the SAA will obviously not start the offensive there it'll definitely be a westward push from the east
The Afghan Rebels weren’t particularly well supplied or unified either, and yet they still managed to hold out in the mountains against the Soviets for almost a decade.
Of course, the mountains in Northern Syria are much less ragged than those of Afghanistan, and the Rebels in the North are probably more exhausted and demoralized as well.
The Afghans still received received regular supplies from Pakistan and had camps there too. Similarly, the strength of the Idlib rebels will be highly dependent on what Turkey does.