What if Constantinople had never fallen to the Turks?

[Ibrahim]

An intersting concept?

What might the results have been. Possibly a city state like Venice etc.,

Could a crumbled state have lasted? the intersting point is that constantinople was the seat of the Greek church, so might it have ended up like the vatican?

What effects would this have had on the spread of Islam and on Greece as a whole?

well, I can answer the last question:

1-wouldn't have made that much of a difference. the Ottomans already had a considerable part of the Balkans in their hands by 1450, and in fact the capital at the time iirc was in Edirne (Adrianopolis).

what the fall of Constantinople did more than anything was add great prestiege to the Ottoman rulers.