Executing the Patriarch, even if he was a clearly partisan actor, seems like something which won't easily be forgotten come peace time.I see a lot of stubbornness in this thread as if it is already a conclusion that Turkey keeps Constantinople. Turkey here has committed atrocities of great magnitude, it has challenged the international order twice, it has allied itself with the most vile regimes and has be shown to be totally untrustworthy. Under no circumstance would the Greeks or the Soviets let them keep it. Some have speculated that the USSR will let Turkey keep the straits in order to control them by proxy, but why would they do that when they can outright control them or influence it better as an international zone.
Comparing the Rhineland, a German state with German customs, culture, and with a homogeneous ethnic group to Constantinople is wrong. This is a Greek Tl, that should at the very least tell you guys what the most likely option will be. If you all insist on Greece falling short as it always had in OTL, why would the author write this. A compromise is most likely, with international zone with multipolar control.