Few analysts, foreign governments or intelligence agencies believe Assad himself faces any fate other than negotiated flight or death at the hands of his own people. But for Western officials, the challenge has become much more complex than forcing Assad out or pushing Russia to abandon him.
One senior Western government source said the most likely outcome might be protracted conflict such as that in 1980s Lebanon, dragging in foreign powers and lasting well over a decade.
Ultimately, much depends on Assad himself. But for all the efforts of Western intelligence services to build up a psychological profile, they say the actions of the British-trained ophthalmologist remain difficult to predict.