The last truly Orthodox Divine Liturgy in the Great Church, the Hagia Sophia in Constantinople, took place December 11, 1452. On December 12, the “Patriarch” Cardinal Isidore (ostensible Patriarch of Kiev and all Russia, though deprived of his see by the Grand Prince of Muscovy, Basil) proclaimed the union of the Eastern Church and the Western described in the document Laetentur caeli, the result of the Council of Florence. All celebration of the Divine Liturgy to follow in Hagia Sophia, to the last celebrated on 29 May 1453 which was interrupted by slaughter of all in the church by the Ottoman Turks, were unionist and not properly Orthodox. It was in fact the opposition of many in Constantinople to the Union of the Council of Florence, initially led by St Mark Eugenikos of Ephesus (spokesman of the Eastern delegation and one of only two participants who refused to sign the council’s proclamation of union), that held off implementation of the union for so long after that non-ecumenical council ended on 6 July 1439.
The acceptance of this council by the Romans, that is the leaders of Constantinople, effected a break in relations with Muscovy, depriving them of badly-needed support in their struggle against the Ottoman Turks. Though the die seems already to have been cast by that time, it might have been the case that the Emperor, in rejecting the union, might have received more help from East than ever he did from West in the final struggle to save what was left of the Roman Emprire. The early modern period in the East might have begun very differently indeed had this been the case.
In this case, Esau sold his birthright for an empty bowl.
But this is only so much wondering over long-spilled milk.