Since the battle of Ankara the Ottomans were divided in two States: 1 in the Balkans and 1 in Anatolia. Mehmed I of Edirne never attacked Constantinople nor did his successors except for Mehmed II but died during the siege ending it. However, Constantine XI was deposed by a popular Orthodox mob led by Gennadius to prevent a union with Rome and ever since 1459 the Town is being ruled by the Patriarch rather than the Emperor.
What if the Ottomans conquered it in 1453 or earlier? Would the Greek Orthodox Church still be dominating public life in Eastern Europe? Would Constantinople have a population in the millions instead of 100,000 now in 2018?