The An Shi rebellion went on for a decade and even managed to capture the Chinese capital, but eventually collapsed because the Tang could wait them out and the Yan dynasty imploded, could the Yan have succeeded and what may have happened after?
Shi (Siming) was fine. But An Lushan's mental and physical issues would pose a challenge.That An Shi personally exploded mentally was a problem as well.
But would it? A Yan victory would help Tibet since China would be incredibly weakened. But an extensive Tibetan occupation could also draw Tibet into an occupation of parts of China Proper that might divert Tibet's resources and also weaken its hand against enemies like the Abbasids.If it succeeded, we could see a Tibet-wank.