I disagree. Allowing the Byzantines to remain powerful is the most dangerous development. The Byzantines are the only state on earth outside the Tang, which could land a death blow to the Umayyad or Abbasid states. A surviving Sassanid empire likewise, would not have the required power to defeat the Muslim power once it captured Iraq, no matter what state the Sassanid had.
A failed invasion of Byzantium would likely lead to Byzantium recovering and defeating the Abbasid near Mosul and capturing Iraq and then the entire stack of cards break. Thus, it is geopolitically imperative that the Islamic State places the Byzantines on their heels and at best, strangles them. No expansion east can safely occur long term without devastating Byzantium and keeping them constantly at war.
My opinion was that the Abbasid avoids the crisis of the 9th century that nearly saw its entire collapse. Thus, the Abbasid hegemony remains in control of the many magnates in Iran, Egypt, Syria, etc and defeat the resurgent Byzantines in Anatolia in the 860s. From there, the Abbasid hegemony is in a similar position in 930 as it was in 830, the hegemony of the near east, North Africa and the west directly outside India and China. By the 10th century, Turkic conquerors arrive and convert to Islam and invade India as otl, in the name of the Abbasids or nominal vassals.
From there, these Turkic armies bolstered by minor Arab retinues, Mamluks, muhjahadeen, etc... make better gains early. So, imagine the Ghurid conquest of Hindustan under various autonomous Mamluks generals, all of whom were vassals of the Abbasid nominally. However, in a scenario where the Abbasid remain the dominant power as it was in 830, this vassalage would be far more tangible.