Hassan's Dissappearance Discussion

"He looked around to to tell Hassan, who he was sure had already seen into his thoughts. Hassan was of course no longer there." (p. 769)

When Kit journies to Lake Baikal via the stone arch of Tushuk Tash, he is accompanied by Hassan, the loyal lieutenant of the Doosra.

Al-Doosra is the "local prophet" who was "driven mad by the desert" (p. 756) and who advocates for a Pan-Turania from Manchuria to Hungary united under a "single Shamanistic ruler" - a Northern Prophet known as "the One who comes. " Hassan and the Doosra are also very into ganga.

What does Hassan's dissappearance mean? You got me.

Here are the relevant sections that I can see:

Auberon Halfcourt: "The future out here simply belongs to the Prophet. It might have gone differently. This madman might have actually founded his pan-shamanic empire." (p. 758)

Lieutenant Prance: "Because this Arch is the Gateway," declared Prance - "unless we enter by way of it, we shall always be on the wrong journey." (p. 764)

Al-Doosra: "I am only a servant in this matter," said the Doosra. "My own master will be found in the north, at his work. If you wish to seek him for yourself, he will receive you." (p. 765)

At Tushuk Tash:

Hassan: "We have nearly completed the journey."
Kit: "And the Prophet? The Doosra's master? Shall I speak to him?"
Hassan: "You spoke to him." (p. 768)

Then Hassan dissappears.

After:
Lieutant Prance: "Out here pilgrimage is a matter of kind and wrathful deities. Timing. Guidance."
Kit: "Waht's that mean?"
Prance: "Ask Hassan."
Kit: "Hassan dissappeared the minute we got to the Lake."
Prance: "Exactly." (p. 774)

OK, so who was Hassan? Who was the Doosra? Who was the Prophet? Why did Hassan disssapear? And why did he leave Kit with more ganga?

Any thoughts?