A lot of searching hasn't found much on this topic, so, here goes:
Manicheaism made a decent shot at becoming a globe-spanning universal religion like Christianity, Islam, or Buddhism - it had adherents as far west as Rome and as far east as China. So, what happens if it manages to take over Persia sometime between its founding and the formation of Islam, and thus develops an actual power base? The method that comes most to mind is by the Hephthalites conquering Sassanid Persia and it coming to power that way (given the excellent Rise of the White Huns TL), but I'm sure there are other paths it could have followed.
Thoughts? It seems like an interesting way to avert the common "no Islam means Christianity reaches the Indus" cliche. Are there any TLs on the subject?