Iran’s proxy Hezbollah is putting boots on the ground. They are much more effective than 30 years ago.
Alawites are only ~10% of the population. Since ISIS is in the habit of slaughtering minorities and Wahabis are not much better Assad has also drawn support from Armenians,Kurds and other minorities. All told about ~27% of the population are minorities(including Alawites).Strategically not ideal, but enough to win with resources and effective leadership.
Time to split Syria in half. The regime can hold on to the coast, Aleppo and Damascus while the Sunnis gets to keep the desert.