the last time I checked (which may have been 1 or more years ago.. not sure) the Syrian army had anywhere between 100k-150k soldiers (not including foreign allied militias like Hezbollah, Iraqis etc... which is around 15k more or less) & while it's true that they have been depleted but remember the other side also has lost alot, not only that but the number of people in government controlled areas is around 13 million so there is quite a large pool to replenish from , if I'm not mistaken the government does not allow men of fighting age to leave Syria, while in Rebel/AlQaeda controlled areas no more than 2 million live there, these civilians are completely demoralized because they are being displaced so Rebels can't replenish as well as the SAA.
1) SAA has max 30.000 troops
2) 80% of Syrian population is sunni muslim and they so hate radical sectarian Assad,Iran and Iran backed shia terrorist groups
3) Syria had 23 million population in 2011 .... over 8 million Syrians moved to Turkey,Iraq,Jordan,Egypt,Lebanon,Europe since 2011 ,,,
there are 4 million Syrians in Idlib
and there are around 2 million Syrians in Turkish Army controlled cities like Afrin,Jarablus,Azaz,Al Bab,Telabyad,Rasulayn,etc
and over 1 million Syrians died since 2011
It is open to debate how serious the military elements of the regime are without the intense support of Iran on the land
Assad Regime forces are far from a military capacity to reclaim all Syrian territory