The title is fairly self-explanatory. How do you create a Europe and for that matter a world stuck in the High Middle Ages for another 1000 years?
I would think the Black Death as a disease dying out before it spread throughout Europe might allow Europe to stay in the High Middle Ages, but another plague could easily do the same or worse to Eurasia.
In addition, the Byzantines need to still be in control of Anatolia to prevent Europeans from circumventing the Ottomans by trying to travel the seas.