Some say Constantinople could be considered to have fallen at the point the soldiers of Mehmed II entered the Hagia Sophia
Legend has it that the priests saying mass at the time the massive doors were battered down simply melted into the walls, and will return to finish their mass when the Hagia Sophia is again a Christian Church.
It is Christ Who will finish the Mass, He Who starts every Mass. The priest are the finger and the tongue, and yes, they will be back.