Steve Coll thinks Assad is finished:
Assad’s coming demise seems less of an argument than an observation. It looks probable that the President will take his place among the war’s victims, at the hands of a coup-maker within his ranks, or else at the hands of a rebel attack, in the manner of Muammar Qaddafi’s death at the climax of Libya’s rebellion. It is conceivable that Assad could slip into exile, perhaps to a dacha outside Moscow, where deposed Soviet clients and spies used to settle into retirement and give the occasional bitter interview to a Western correspondent back during the Cold War.
Max Fisher is unsure:
[T]here is a long history of rebel groups breaching a capital city, or even killing top regime officials, and ultimately losing. Three of the bloodiest, nastiest civil wars of the 1990s saw days like today, and all three ended with the government staying in power and the rebels, for all their bombings and advances, defeated. Though is none identical to Syria's, of course, just as all wars are unique in their own unhappy way, the conflicts of Algeria, Sri Lanka, and El Salvador show that Assad would have precedent for hanging on.
Paul Mutter worries about the regime's reaction to the bombing:
Rula Amin of Al Jazeera reports that there is "[a]nxiety in Damascus as people anticipate a strong govt reaction against the armed rebels on the ground."…There is indeed reason to fear that this attack will lead to reprisals. In the regime's collective mind, this simply cannot go unanswered. A major new military push against the rebels, if it occurred, could be damaging to them if in their recent push towards Damascus they are stretching their forces too thin.
Earlier reaction to today's events here.