John, if he is allowed to keep these areas, he wont stop there, he will trump up some other excuse to continue. A big mistake of the allies was to start scaling down their troops in Germany, thereby making it vulnerable. After all, he could claim East Germany was always Russian.
Dont forget all the ex Soviet states also, the communists "seeded" Russians in all those states for many years. I recall my recent company employing a Kazak national as a representative, but she always described herself as Russian so as to differentiate herself from native Kazaks, despite the fact she was something like third or fourth generation Russian.