The rules state; "The game ends at the end of a complete turn following the turn in which a certain number of Empty City markers have been played on the board." Let's assume 4 players are playing, therefore the endgame condition call for 14 empty city markers to be placed.
A. If later in that round someone urbanizes an empty city and takes the number back below 14, thereby removing the empty city marker, does the game still end the following round?
B. Or in the following round someone urbanizes does the game still end that round?
I'm assuming the answer will be the same for each. Since the rules don't seem to address that, we've been going on the assumption that since the last Empty City marker was placed and the rules don't address the issue of urbanizing afterward, that the game still ends as normal.
"Nothing in Biology Makes Sense Except in the Light of Evolution" - Theodosius Dobzhansky
There is grandeur in this view of life, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
The answer is yes, once the game end is triggered urbanization cannot undo it.