The Western Allies (Truman and Churchill) are NOT going to pull out of Germany. Not only do they not trust Stalin, but they are going to hunt down and try theNazi war criminals. Besides the fact that the German infrstructue has been destroyed and needs rebuilt.
It's kind of a moot point given the information indicating the Soviet Union could not have constructed enough nuclear weapons and bombers for the fait accompli the OP needs, but the reason they didn't trust Stalin was because he reneged on the commitments he had made to the Wallies. The whole point of this scenario is (or was) what if he had kept the agreements and they had then withdrawn as intended after the top Nazis have been caught, etc.