We don't know presently what the sequence of events were but I strongly suspect as mooted below, that when Assad reached for the Army it just wasn't there: that major players in the military hierarchy had been already purchased.

Faced with that it didn't matter about any foreign assistance as there was nothing: no Syrian military to actually assist.
He decided it was game over as whatever part of the army still faithful to him were nowhere near enough and that he might destroy Syria in a war he was bound to lose...thus his decision to exit. You can call that "cowardly" if you wish but perhaps the idea was with him gone it might save the country from further trauma?


Alas...Assad taking himself out the picture hasn't improved anything: with any existing air cover gone its free bombing for Israel...which has decided to "Demilitarise" Syria completely no matter who left or what faction was likely to be in charge...and looking at the passport service up in smoke, they are apparenty now moving on to destroying the civil infrastructure and bureaucracy too with what looks like the aim of creating a permanent failed state.

Meanwhile the land of Syria: one of the cradles of civilisation looks likely to become a mere rehashed canvas backdrop for a savage Jahadi faction war with the US and Turkey clearly arming funding and thus controlling several headchopping outfits each.

-The future looks seriously awful for Syrians.