How would things have developed in Syria if these areas had become independent states?
You mean like they were briefly, before Aleppo and Damascus merged and then annexed the other bits, except where stopped by external forces?
There was too much pan-Syrian sentiment at the time. Unless someone (probably France) enforces the separation, these states will naturally tend to merge together - that includes, by the way, Lebanon, as well as Palestine and Transjordan.
Wasn´t it more pan-Arab sentiments?
Why were the other entities, like the Alawite and Druze state, not able to survive? Did the French put less effort into making them survive than they did with Lebanon?