Assad is an Alewite, which is a Shiite sect. Trust the upper ranks, pilots and key personnel in the military were Alewite or Shiite.
Syria is almost 70% Sunni Muslim. This percentage was probably reflected in Assad’s infantry and those Sunni’s long ago deserted.
You can hold territory without infantry. Assad can’t make gains and hold them.
This could go on for decades.
Make that:
You can’t hold territory without infantry.
Assad needs to set up a rump state on the coast with Damascus and Aleppo in it. Offer truce to rebels if they leave Aleppo. Then the rebels can hold on to the rest of the country in the desert and name their nation Jihadstan.